How long did the Follow Through educational program last?

Follow Through was the largest and most expensive experimental project in education funded by the U.S. federal government that has ever been conducted. The most extensive evaluation of "Follow Through" data covers the years 1968–1977; however, the program continued to receive funding from the government until 1995. "Follow Through" was originally intended to be an extension of the federal "Head Start" program, which delivered educational, health, and social services to typically disadvantaged preschool children and their families. The function of "Follow Through", therefore, was to provide a continuation of these services to students in their early elementary years.

Follow Through (project)

In President Lyndon B. Johnson's 1967 state of the union address, he proposed $120 million for the program, to serve approximately 200,000 children from disadvantaged backgrounds. However, when funding for the project was approved by the United States Congress, a fraction of that amount—merely $15 million—was authorized. This necessitated a change in strategy by the Office of Economic Opportunity (OEO), the government agency charged with oversight of the program Instead, program administrators made the "brilliant decision... (to) convert "Follow Through" from a service program to a research and development program".

"Follow Through" planners felt that they were responding to an important challenge in the education of disadvantaged students. It was generally hypothesized that the mere provision of specific supports in the form of federal compensatory programs—such as "Head Start" and Title I of the Elementary and Secondary Education Act—would result in increased academic achievement for disadvantaged children, if implemented faithfully by committed teachers. However, studies had shown that despite its successes, in general any gains that children made from "Head Start" (in measures of academic achievement) "faded out" during the first few years of elementary school. It was unclear to policy makers and others if the elementary school experience itself caused this phenomenon, or if specific approaches to instruction within schools were the problem. "Follow Through" intended to solve the problem by identifying what whole-school approaches to curriculum and instruction worked, and what did not. Subsequently, effective models were to be promulgated by the government as exemplars of innovative and proven methods of raising the academic achievement of historically disadvantaged students.

Conceived and implemented in the midst of President Johnson's War on Poverty campaign of the 1960s, "Follow Through" "came out of larger plan which attempted to lay out the causes and cures of poverty in American society on a systemic basis". In addition to the landmark Elementary and Secondary Education Act of 1965, other initiatives included economic policies designed to maintain levels of high employment and federally subsidized job training specifically targeted at people from disadvantaged backgrounds. These programs were implemented amidst the turbulent era of the 1960s and 1970s; marked by the struggles and eventual enfranchisement of a number of formerly excluded constituencies "including African Americans, feminists, Hispanics, Native Americans, and parents of handicapped children".

In typical scientific experiments, treatment and control groups are selected through random assignment. Because "Follow Through" was an experiment designed to evaluate the efficacy of a number of interventions in local districts, districts chose the interventions they wanted implemented in their schools. This method of selecting a desired intervention among several candidates is called planned variation. One publication refers to it as "random innovation". Actually, there is nothing random about it. Planned variation was thought to be advantageous over random assignment because it gave local communities (e.g. community members, parents, administrators, and teachers) an element of local control over the implementation of their program. In fact, Hill believed that programs like "Follow Through" "can be... permanent sources of advocacy pressure on behalf of the goals and beneficiaries of federal programs".

"Follow Through", like "Head Start", was enormous in scope, and designed to remedy the fact that "poor children tend to do poorly in school". Despite the cut in funding, it nevertheless served a substantial number of students. At its height, the program would grow to encompass 20 different sponsored interventions and approximately 352,000 "Follow Through" and comparison children in 178 projects nationwide.

In addition to identifying the most effective instructional practices and disseminating them to schools and districts, it was also hoped that "Follow Through" would help reduce the number of potentially conflicting federal intervention programs in schools, which was thought by some to be counterproductive and expensive. Moreover, if models could be identified that were effective with needy children, these interventions could be staged in regular education classrooms as well.

Because "Follow Through" came into existence because of executive and not legislative action, overall control for the program rested in Johnson's Office of Economic Opportunity (OEO), which spearheaded Johnson's War on Poverty policy. A major component of the policy was community involvement. The Community Action Program (CAP) was charged with fulfilling this function through the establishment of local agencies and programs that carried out various federally sponsored initiatives for disadvantaged populations. However, CAP (and, to some extent, OEO) fell into disrepute among legislators and others, because "it resulted in the political mobilization of the poor and the undermining of local government agencies". "Follow Through" was intended to be an extension of the "Head Start" community action program. Since "Head Start" was politically popular, a program associated with "Head Start" would put the OEO "back in the good graces of Congress". Although "Follow Through", like "Head Start", was initially intended as a social action program, the decision to transform "Follow Through" from a social action program to a social experiment was not correspondingly changed in the congressional legislation.

"Head Start" personnel remained involved in the design and implementation of "Follow Through", although it appeared they were working at separate ends from the planning group of the OEO, who viewed "Follow Through" as an empirical investigation. Much of what occurred during the planning stage—which Egbert describes "as a time of haste and confusion"—was an attempt to satisfy constituencies of both perspectives.

Due largely to the sociocultural context in which "Follow Through" was born, planners deliberately structured the program to minimize the involvement of federal officials in the implementation effort. The more "Follow Through" could be perceived as a locally controlled effort, the better. OEO hoped "idealistically" that "Follow Through" could satisfy both empirical and social action purposes.

It seems doubtful that any form of experiment could realistically and faithfully serve both aims. According to Hill, true program evaluators should be "technical rather than political or programmatic, and their attitudes skeptical and dispassionate". The planning group of OEO wanted a true empirical investigation that would determine the most effective models. Conversely, CAP and "Head Start" personnel advising the "Follow Through" planners viewed it as a social program. Thus, "neither set of constituent groups was fully satisfied with this solution".

In addition to the planners of "Follow Through" having conflicting views on the real purpose of the program, the selection of sponsors was equally imprecise. "Follow Through" sponsors were an eclectic mix of individuals or groups conducting research on instructional methods. Some came from universities, including schools of education. Others were involved in private or grant-based research efforts. The selection method was unclear. According to Watkins, "invitations were apparently extended to any group conducting research on instructional methods".

Some of the sponsors had fairly well developed interventions based on theories of instruction. Others merely had ideas for what might constitute effective interventions. The sponsors also differed widely on the outcomes they expected as a result of their programs. Some sponsors had very specific goals which they believed would lead to very specific outcomes, such as improved literacy skills on measures of reading achievement. Others had more general goals, such as increased self-esteem, or heightened parental involvement in schooling. Most of the programs were in a very early stage of development and had not been extensively (or even moderately) field-tested or piloted. Some programs were so ambiguous that Elmore wrote that "most program developers were simply not clear what their programs would actually look like in a fully operational form". Many sponsors could not explain precisely which aspects of their models would lead to the stated outcome goals of the model.

Despite ambiguities among many of the models (and the minute shades of distinction between some models) the "Follow Through" literature classified models according to the degree of structure they offered, and where they place emphasis on learning.

The "degree of structure" (e.g. "low", "medium", or "high") offered by a particular model is evidenced by how closely teachers were instructed to adhere to specific procedures, including: ways of arranging the classroom and delivering instruction, the degree of interaction between adults and children, the level of parental involvement, and so forth. Below are brief examples of two models that represent extremes of the spectrum.

Direct Instruction model. Developed by Siegfried Engelmann and Wesley Becker of the University of Oregon, direct instruction is scripted and specifies precisely what the teacher says and what the students' responses should be. Moreover, the program designers carefully sequenced the instruction so that students do not progress to higher-order skills unless they have mastered prerequisite basic skills. There is a high degree of interaction between teachers and students so the teacher may receive continuous feedback about how well the students are doing, and adjusts instruction accordingly. The program makes a specific distinction between on-task and off-task behavior: instruction is arranged so that students are fully engaged in learning (via frequent checking for understanding and praises by the teacher) the majority of the time. According to the program sponsors, anything presumed to be learned by students must first be taught by the teacher.

Bank Street model. The Bank Street model was developed by Elizabeth Gilkerson and Herbert Zimiles of the Bank Street College of Education in New York. In this model, the students themselves direct learning: they select what tasks they wish to engage in, alone or with peers. The teacher arranges the classroom in ways that the sponsors believe will create the conditions for successful learning: various objects and media are available for children to interact with, and the teacher acts as a facilitator, guiding students through activities. According to the program sponsors, students use previously learned knowledge to construct new knowledge. According to the sponsors, given a safe and stable environment, learning is a process that occurs naturally.

In his evaluation of the operational facets of "Follow Through", Elmore expressed concern that the shades of distinction among models in terms of structure made comparisons and final analysis among models problematic. Descriptions of the interventions derived from the sponsors themselves. There was no other reliable source from which the program administrators could obtain information about them. Had they been able to see examples of the different models being implemented, they might have been able to ask clarifying questions in order to better distinguish between them—which might have been important for purposes of assessment.

Program models were also classified by where they place emphasis on learning, according to three educational orientations: basic skills, cognitive conceptual skills, and affective/cognitive behavior (also see Appendix A).Despite the differences, there were points of agreement among all sponsors. Sponsors agreed that their interventions should be developmentally appropriate—that is, models take account of where students are in their development as learners. Second, everyone agreed that teaching and learning should be responsive to the needs of individual learners. Third, they agreed that all students—even those from the most disadvantaged backgrounds—could learn to the level of their more fortunate peers. Fourth, classroom management procedures that create an appropriate learning environment should be emphasized. Fifth, school should be a place where students experience both high self-esteem and academic success. Ironically, the last point of agreement—as far as Maccoby and Zellner were concerned—was that all interventions should have very clear objectives about the content and skills that students should know and be able to do. This last detail is worth noting for two reasons. First, the program outcome goals that were provided by sponsors appeared relatively broad. For example, the sponsors of the Tucson Early Education Model explain that "there is relatively less emphasis on which items are taught and on the transmission of specific content, and more emphasis on 'learning to learn'". Likewise, teachers of the Cognitive Curriculum design their own approaches to instruction (including the specification of learning goals), with assistance from sponsors and fellow staff members. While the outcome goals might commonly be described as high levels of academic achievement or mastery of basic and higher-order thinking skills, exactly how students demonstrate these skills is missing in the "Follow Through" literature. During sponsor meetings, there were several heated arguments between some sponsors about the degree of specificity to which they should link facets of their models to student outcomes or behaviors. "Follow Through" administrators could not investigate models more thoroughly because of limited time; indeed, only eight months separated the selection of the sponsored model approach and the start of the experiment. Because Congress had already reduced the program budget, there was legitimate concern among planners that a delay in implementation could be disastrous to the program. Another reality was simply the lack of alternate interventions. Because such a large-scale experiment in education had never been done before, the Office of Education had no arsenal of interventions to try out.

Selection of "Follow Through" implementation sites proceeded in concert with the selection of models. With the assistance of various state and federal education agencies, 100 communities were invited to apply to the program, based on criteria established by the OEO. According to Egbert, 90 districts applied, of which 30 were chosen for participation in "Follow Through". However, due to pressure from influential politicians, additional sites were later added. Not coincidentally, the inclusion of several additional districts appears to have been an attempt to satisfy a number of local political figures by including their communities in the program.

While Elmore laments that sites could have been chosen with a greater degree of scientific rigor (e.g. stratified random sampling), this was impossible, for at least two reasons. First, "Follow Through" administrators had the obligation to select a minimum number of sites with "Head Start" programs, because the ostensible purpose of "Follow Through" was to complement "Head Start". Second—aside from political pressures—communities had to be willing participants in the process (ostensibly) to preserving the fidelity of the implementations. On this point, Elmore tends to agree.

Because of the range of models, a broad range of instruments and analytical methods was selected in order to measure the targeted outcomes of basic skills, affective behavior, and cognitive behavior. Adams and Engelmann wrote, "while critics have complained about test selection and have usually suggested more testing, the assessment effort in this study went well beyond any other educational study conducted before, or since". In all, 14 instruments were selected and administered at various times throughout a student's participation in "Follow Through". Three groups of students, known as Cohorts (i.e., Cohorts I, II, and III) were followed longitudinally from the time they entered "Follow Through" (e.g., Kindergarten or Grade 1) until they exited the program (Grade 3). While the authors of the "Follow Through" report rated the instruments as having high reliability, some sponsors questioned the validity of the instruments in measuring the varied orientations of the models. Other critics, such as House "et al." in a Ford Foundation-funded and widely disseminated analysis, also criticized the instruments. However, the evaluators believed that the instrument battery represented the "best compromise" given the range of models. Despite the relatively large number of students who participated in "Follow Through", the evaluators imposed rigorous restrictions on the sample that was actually in the statistical analysis. The comparison group—students from the community identified as not participating in "Follow Through"—was not subject to precisely the same restrictions as the control group, as long as they entered and exited school in the same districts and at the same time as "Follow Through" students.

Due to the number of intervention sites and range of instruments the analysis was complex and extensive. According to Watkins, there were over 2,000 comparisons between "Follow Through" and non-"Follow Through" groups alone. In 1968, Stanford Research Institute (SRI) was awarded the contract for the "Follow Through" evaluation. However, due to a variety of factors—including, perhaps, SRIs underestimation of the complexity involved in such a comprehensive analysis—Abt Associates, Inc. later inherited the evaluative duties in the summer of 1972. The summary of results, entitled "Education as Experimentation: A Planned Variation Model" was published in 1977.

The empirical goal of the "Follow Through" evaluation was to determine which models were effective in raising student achievement in the three domains as evidenced by positive effects using the selected instruments. Within models, the evaluators compared performance on the various instruments between "Follow Through" (FT) and non-"Follow Through" (NFT) comparison groups at each site. Within groups, the evaluators averaged students' scores on each measure (or outcome variable) in order to yield a "group" score. Thus, the group scores of FT students were compared to the group scores of NFT students. An important—and later controversial—statistical adjustment technique was employed by the evaluators in order to "improve the integrity of the results". Because there were differences between treatment and comparison groups (e.g. the average score on an outcome measure for a NFT group might have been higher than the corresponding average score for a FT group), the evaluators employed a statistical method known as analysis of covariance (ANCOVA) in order to adjust for these and other differences. The difference between the FT and NFT students was then used to measure the effects of a given model. Sites where models met the criterion for "educational effectiveness" were assigned a value of 1; negative effects were assigned -1; and null effects—"insignificant educationally, statistically, or both"—were assigned a zero. According to Elmore, adjusted results using the ANCOVA technique should be interpreted cautiously for two reasons. First, ANCOVA "is not a substitute for random assignment, but it has become a conventionally accepted technique for handling initial group differences in quasi-experimental data". Second, the larger the initial differences between treatment and control groups, the weaker the strength of the results.

The results of "Follow Through" did not show how models that showed little or no effects could be improved. But they did show which models—as suggested by the less than ideal conditions of the experiment—had some indications of success. Of these models, Siegfried Engelmann's Direct Instruction method demonstrated the highest gains in the comparative study. The most notable critique of "Follow Through" (described in detail below) takes issue with the fact that the models which showed positive effects were largely basic skills models. Abt Associates identified five major findings related to the question of differential model effectiveness; the principal empirical findings of the experiment were reported as follows:

A separate analysis examined the impact of Siegfried Engelmann's Direct Instruction method on students over several decades. This analysis suggested a long term benefit.

Wisler "et al", in their review of the "Follow Through" experience, wrote that it was likely that no other educational data has been examined more extensively, excepting the Equality of Educational Opportunity Survey. At least three major reevaluations of the "Follow Through" data exist in the literature: House, "et al." (1978); Bereiter and Kurland (1981); and Kennedy (1981). All largely confirm the original statistical analysis conducted by Abt Associates. Generally, the consensus among most researchers is that structured models tended to perform better than unstructured ones, and that the Direct Instruction and Behavior Analysis models performed better on the instruments employed than did the other models.) Most critiques of the "Follow Through" experiment have tended to focus on the operational and design problems that plagued the experiment. In particular, these critiques note that there was more variation within a particular model than there was from model to model. This problem has largely been attributed to the problem of how to measure the effectiveness of a particular implementation; the measures used were largely qualitative and anecdotal. In some instances, sites were included in the analysis that had ceased to implement specific models, or the model sponsors had serious reservations about the way particular models were implemented.

The most vocal critique was the House, "et al." (1978) reanalysis. The article—along with several rebuttals from the original evaluation team and other researchers—was published by the Harvard Educational Review in 1978. The authors were extremely dissatisfied with the pronouncement of the evaluators that the basic skills models outperformed the other models. The authors approach the critique on the assumption that basic skills are decidedly just that—basic. The authors imply that basic skills are only taught through "rote methods"—a decidedly negative connotation (p. 137).
Regarding the finding that "models that emphasize basic skills produced better results on tests of self-concept than did other models", the authors question the efficacy of the self-esteem measures; implying, among other things, that young students cannot possibly have a concrete understanding of self-concept (pp. 138–139). While the article intended to review the operational design of the "Follow Through" evaluation, instead it appears to (1) refute the finding that cognitive-conceptual and affective-cognitive models were largely failures, and (2) unilaterally condemn the models that emphasize basic skills. The implication is that the goal of education should not be increased student achievement in solely basic skills, and that "Follow Through" would have been better employed to discover how measures of all three orientations could be made successful. Absent from the critique is the finding that, for third graders, only the Direct Instruction model demonstrated positive effects in all three domains, and that one of the remaining two models (Behavior Analysis; the other was the Parent Education model) that had positive effects in at least two domains was also a self-described "basic skills model".

In 1972, the OE created the Joint Dissemination Review Panel (JDRP) and the National Diffusion Network (NDN) to disseminate information about effective models to schools and districts nationwide. JDRP reviewed programs for effectiveness according to a mixture of empirical and holistic criteria. NDN was responsible for disseminating the results based on the recommendations of JDRP. Watkins (1997) criticizes the dissemination criteria for two reasons. First, the organizations identified programs for dissemination that had not been part of the "Follow Through" experiment and for which there was no empirical validation. Second, JDRP and NDN endorsed programs that showed improvement in areas "such as self-concept, attitude, and mental or physical health (of students)... (or) if it has a positive impact on individuals other than students, for example if it results in improved instructional behavior of teachers" (p. 47), but did not raise students' academic achievement. Thus, programs "that had been incapable of demonstrating improved academic performance in the "Follow Through" evaluation" were recommended for adoption by schools and districts. Watkins cites the former Commissioner of Education, Ernest Boyer, who wrote with dismay that "Since only one of the sponsors (Direct Instruction) was found to produce positive results more consistently than any of the others, it would be inappropriate and irresponsible to disseminate information on all of the models".

Of course, it would have been ideal to have the kind of conclusiveness associated with laboratory experiments when we conduct social experiments in communities and schools. Andy B. Anderson (1975) wrote that "the idea of a controlled experiment has long been recognized as a goal worth pursuing in the social and behavioral sciences for the same obvious reason that made this mode of inquiry the predominant research strategy of the natural and physical sciences: the controlled experiment permits the most unequivocal assessment of a variable's influence on another variable". Particularly when experimentation is used as a tool for informing policy decisions (e.g., in recommending the efficacy of some instructional approaches with disadvantaged students over other, less effective interventions), the design should be of the highest degree of rigor possible. For a variety of reasons, "Follow Through" did not have the classic characteristics of a true experiment.

Lack of systematic selection of interventions and lack of specificity of treatment effects. Due to a variety of circumstances detailed earlier, the "Follow Through" programs were not systematically developed or selected according to any type of uniform criteria. Given more time, sponsors may have been able to better identify the types of treatment effects that an observer might expect to occur under controlled conditions. More importantly, program sponsors might also have been required to show those specific facets of their interventions (e.g., particular pedagogical techniques) which would produce the intended effects. Despite these flaws, the sponsors agreed on being subject to the same evaluation instruments. Unfortunately, the instruments shed little light on what about the ineffective programs made them so unsuccessful. The converse is also true. Since structured programs tended to show better effects than the unstructured ones, it would appear logical that efforts might have been made to identify commonalities among the effective structured programs. These shared characteristics might have informed the development of additional effective programs or made the ineffective approaches better. Starting in 1982, funding was in fact reduced for those programs that were identified as successful in "Follow Through", perhaps on the presumption that funding would be better diverted to assisting failed programs. Ultimately, programs that had lesser empirical validation were nonetheless recommended for dissemination along with the successful models.

Lack of random assignment. Random assignment of subjects into treatment and control groups is the ideal method of attributing change in a sample to an intervention and not to some other effect (including the pre-existing capabilities of students, teachers, or school systems). However, for a variety of practical reasons, this procedure was not done in "Follow Through". Instead, sites were selected "opportunistically", based on their readiness to participate in the evaluation, and on their unique circumstances of need. As Stebbins "et al." point out, the treatment groups were often the neediest children. To randomly select some of the most disadvantaged children (many of whom participated in Head Start prior to "Follow Through") out of the evaluation would certainly have been negatively perceived by community members. Stebbins "et al." point out that there were "considerable variations in the range of children served"; yet despite the presence of "many of the problems inherent in field social research...evaluations of these planned variations provides us with an opportunity to examine the educational strategies under real life conditions as opposed to contrived and tightly controlled laboratory conditions".

Narrowness of instruments. Adams and Engelmann note that many critics have suggested that more instruments should have been used in the "Follow Through" evaluation. Egbert agrees with Adams and Engelmann that the data collection efforts were extensive. Despite the agreement among model sponsors on a uniform set of instruments to evaluate the effectiveness of their models—that model sponsors believed their programs achieved gains on more intrinsic, less measurable indicators of performance, such as increased self-worth or greater parental involvement. To the extent that these desired outcomes occurred, and benefited the lives of students in ways that might never be measurably through quantitative means, those aspects of many models were successful. Both the House "et al." critique and others (cited in Wisler) express concerns about the inadequacy of the instruments used to measure self-esteem the "Follow Through" evaluation (i.e., the Intellectual Achievement Responsibility Scale (IARS) and the Coopersmith Self-Esteem Inventory). But it was better, according to many researchers, to measure outcomes imperfectly rather than not to measure them at all. Thus, while "perfect" measures of desired outcomes might never exist, one should not let the perfect be the enemy of the good—in other words, one could call into question the efficacy of conducting any experiment at all on the basis that some bias or imperfection exists.

Was "Follow Through" a social or scientific program? After an initial period, new regulations mandated that 80 percent of "Follow Through" funding was to be allocated to the provision of service while 20 percent was to be used for knowledge production. The regulations themselves suggest that "Follow Through" was principally "a federally funded education program which contained a built-in research component". An inevitable conflict exists when one attempts to operationalize a federal program in education that possesses both service delivery and research and development objectives. Rivlin "et al." point out that "the byzantine complexity of the public policymaking process makes the conduct of social experiments extremely difficult". Given the reduction in funding, the decision to engage in an effort to evaluate the effectiveness of various interventions in an empirical experiment appears appropriate and straightforward. However, if the change is not reflected in Congressional legislation or communicated clearly at the local level, issues of implementation and conflict with deeply held values inevitably result. There is much evidence that indicates confusion about the intent of the "Follow Through" evaluation at the administrative level.

Issues of local control. The planned variation aspect of "Follow Through" was thought to be beneficial—perhaps superior—to other forms of experimentation (e.g., selection of sites based on randomized assignment) because it would give local communities and schools an element of ownership integral to the successful implementation of the models. Despite the planned variation design, local communities in many sites were nevertheless deeply critical of the program. In some ways, criticism of "Follow Through" had preceded directly from Head Start. Ostensibly, the social service purpose and goals of the Head Start program were clearer than those of the "Follow Through" evaluation. Nevertheless, community leaders had felt that Head Start did not give enough decision-making responsibility to parents and community members. Local interests wanted to make curricular decisions, including the changing of facets of some program models Evans cautioned that "educational communities and contexts vary", which can have a direct effect on the implementation of a model. More problematic, however, is Elmore's and Hill's assertions that the "Follow Through" models interfered with local teaching methods and practices. As Elmore writes, "for "Follow Through", the problem was how to implement program variations in a system where most day-to-day decisions about program content are made at the school or classroom level". Rhine "et al." suggest that it is difficult to get teachers to modify their behavior. And if the objective of changing behavior is achieved, teachers feel little ownership on the model—a decidedly dubious investment. What inevitably seems to happen is that teachers reject programs outright, while others "surrender to the program".

The "fact-value dichotomy". Ernest R. House, co-author of the 1978 critique of the "Follow Through" evaluation, penned an article about what he calls the "fact-value dichotomy" in social experimentation and educational research: "the belief that facts refer to one thing and values refer to something totally different". House elucidates the writings of Donald Campbell, a researcher in the field of evaluation. House noted that, according to Campbell, facts cannot exist outside the framework of one's values because inevitably, an investigation that uncovers a certain fact is either consistent with the researcher's internal values or against them. What results is a difficult choice: the researcher must either reject the fact, or modify his or her value to accommodate the fact. Campbell also believed, according to House, that values—as opposed to facts—could be chosen rationally. House agrees with Campbell's assertion in part, but departs from Campbell in that he believes that facts and values cannot exist in isolation; rather, they "blend together in the conclusions of evaluation studies, and, indeed, blend together throughout evaluation studies". House suggests that the reader envision facts and values as existing on a continuum from "bute facts to bare values". Accordingly, rarely do "fact claims" or "value claims" fall entirely at one end of the spectrum or the other. House provides examples: "Diamonds are harder than steel" might fall at the left of the spectrum, while "Cabernet is better than Chardonnay" falls to the right. In conclusion, House proposes an entirely a new method of empirical investigation called "deliberative democratic evaluation". In it, evaluators arrive at "unbiased claims" through "inclusion of all relevant stakeholder perspectives, values, and interests in the study; extensive dialogue between the evaluator and stakeholders...and extensive deliberation to reach valid conclusions in the study". House decries the use of entirely rational methods when applied to evaluations; indeed, he recommends a degree of subjectiveness, because evaluations like "Follow Through" cannot exist outside deeply held values.

Hill writes: "There is seldom anyone at the local level whose commitment to an externally-imposed curricular innovation, planning process, or financial management scheme springs spontaneously from deeply held personal values." House argues that all decision-making that stems from evaluations in education is the result of a compromise. Watkins argues that "Follow Through" resulted in a clash over values based on different beliefs about how children learn, which can be boiled down to "natural growth" or "unfolding" theories versus. theories of "changing behavior". Watkins asserts that most education experts today do not judge programs by their relative effectiveness with different student populations, but rather by their "congruence with prevailing philosophies of education".


What's a PPO?

In health insurance in the United States, a preferred provider organization (PPO), sometimes referred to as a participating provider organization or preferred provider option, is a managed care organization of medical doctors, hospitals, and other health care providers who have agreed with an insurer or a third-party administrator to provide health care at reduced rates to the insurer's or administrator's clients.

Preferred provider organization

A preferred provider organization is a subscription-based medical care arrangement. A membership allows a substantial discount below the regularly charged rates of the designated professionals partnered with the organization. Preferred provider organizations themselves earn money by charging an access fee to the insurance company for the use of their network (unlike the usual insurance with premiums and corresponding payments paid either in full or partially by the insurance provider to the medical doctor). They negotiate with providers to set fee schedules, and handle disputes between insurers and providers. PPOs can also contract with one another to strengthen their position in certain geographic areas without forming new relationships directly with providers. This will be mutually beneficial in theory, as be billed at a reduced rate when its insureds utilize the services of the "preferred" provider and the provider will see an increase in its business as almost all insureds in the organization will use only providers who are members. PPOs have gained popularity because, although they tend to have slightly higher premiums than HMOs and other more restrictive plans, they offer patients more flexibility overall.

In 1980, an early PPO was organized in Denver at St. Luke's Medical Center at the suggestion of Samuel Jenkins, an employee of the Segal Group who consulted with hospitals for Taft-Hartley trust funds. By 1982, 40 plans were counted and by 1983 variations such as the exclusive provider organization has arisen. In the 1980s, PPOs spread in cities in the Western United States, particularly California due to favorable state laws.

Other features of a preferred provider organization generally include utilization review, where representatives of the insurer or administrator review the records of treatments provided to verify that they are appropriate for the condition being treated rather being largely, or solely, being performed to increase the number of people due. Another near-universal feature is a pre-certification requirement, in which scheduled (non-emergency) hospital admissions, and in some instances, outpatient surgery, must have the prior approval of the insurer and must often undergo "utilization review" in advance.

A PPO is a healthcare benefit arrangement that is similar to an exclusive provider organization (EPO) in structure, administration, and operation. Unlike EPO members, however, PPO members are reimbursed for using medical care providers outside of their network of designated doctors and hospitals. However, when they use out-of-network providers PPO members are reimbursed at a reduced rate that may include higher deductibles and co-payments, lower reimbursement percentages, or a combination of these financial penalties. EPO members, on the other hand, receive no reimbursement or benefit if they visit medical care providers outside of their designated network of doctors and hospitals. (Some, but not all, EPOs do allow partial reimbursement outside of the network in emergency cases.)

Preferred provider organization


Who discovered lanthanum?

Lanthanum usually occurs together with cerium and the other rare earth elements. Lanthanum was first found by the Swedish chemist Carl Gustav Mosander in 1839 as an impurity in cerium nitrate – hence the name "lanthanum", from the Ancient Greek "λανθάνειν" ("lanthanein"), meaning "to lie hidden". Although it is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as lead. In minerals such as monazite and bastnäsite, lanthanum composes about a quarter of the lanthanide content. It is extracted from those minerals by a process of such complexity that pure lanthanum metal was not isolated until 1923.

Lanthanum

Lanthanum is a chemical element with symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. It is also sometimes considered the first element of the 6th-period transition metals, which would put it in group 3, although lutetium is sometimes placed in this position instead. Lanthanum is traditionally counted among the rare earth elements. The usual oxidation state is +3. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.

Lanthanum compounds have numerous applications as catalysts, additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in lighters and torches, electron cathodes, scintillators, GTAW electrodes, and other things. Lanthanum carbonate is used as a phosphate binder in cases of renal failure. It is also an element in the 6th period and in the 3rd group.

Lanthanum is the first element and prototype of the lanthanide series. In the periodic table, it appears to the right of the alkaline earth metal barium and to the left of the lanthanide cerium. Lanthanum is often considered to be a group 3 element, along with its lighter congeners scandium and yttrium and its heavier congener, the radioactive actinium, although this classification is sometimes disputed. Similarly to scandium, yttrium, and actinium, the 57 electrons of a lanthanum atom are arranged in the configuration [Xe]5d6s, with three valence electrons outside the noble gas core. In chemical reactions, lanthanum almost always gives up these three valence electrons from the 5d and 6s subshells to form the +3 oxidation state, achieving the stable configuration of the preceding noble gas xenon. Some lanthanum(II) compounds are also known, but they are much less stable.

Among the lanthanides, lanthanum is exceptional as it does not have any 4f electrons; indeed, the sudden contraction and lowering of energy of the 4f orbital that is important for the chemistry of the lanthanides only begins to happen at cerium. Thus it is only very weakly paramagnetic, unlike the strongly paramagnetic later lanthanides (with the exceptions of the last two, ytterbium and lutetium, where the 4f shell is completely full). Furthermore, since the melting points of the trivalent lanthanides are related to the extent of hybridisation of the 6s, 5d, and 4f electrons, lanthanum has the second-lowest (after cerium) melting point among all the lanthanides: 920 °C. The lanthanides become harder as the series is traversed: as expected, lanthanum is a soft metal. Lanthanum has a relatively high resistivity of 615 nΩm at room temperature; in comparison, the value for the good conductor aluminium is only 26.50 nΩm. Lanthanum is the least volatile of the lanthanides. Like most of the lanthanides, lanthanum has a hexagonal crystal structure at room temperature. At 310 °C, lanthanum changes to a face-centered cubic structure, and at 865 °C, it changes to a body-centered cubic structure.

As expected from periodic trends, lanthanum has the largest atomic radius of the lanthanides and the stable group 3 elements. Hence, it is the most reactive among them, tarnishing slowly in air and burning readily to form lanthanum(III) oxide, LaO, which is almost as basic as calcium oxide. A centimeter-sized sample of lanthanum will corrode completely in a year as its oxide spalls off like iron rust, instead of forming a protective oxide coating like aluminium and lanthanum's lighter congeners scandium and yttrium. Lanthanum reacts with the halogens at room temperature to form the trihalides, and upon warming will form binary compounds with the nonmetals nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon and arsenic. Lanthanum reacts slowly with water to form lanthanum(III) hydroxide, La(OH). In dilute sulfuric acid, lanthanum readily forms the aquated tripositive ion : this is colorless in aqueous solution since La has no f electrons. Lanthanum is the strongest and hardest base among the lanthanides and group 3 elements, which is again expected from its being the largest of them.

Naturally occurring lanthanum is made up of two isotopes, the stable La and the primordial long-lived radioisotope La. La is by far the most abundant, making up 99.910% of natural lanthanum: it is produced in the s-process (slow neutron capture, which occurs in low- to medium-mass stars) and the r-process (rapid neutron capture, which occurs in core-collapse supernovae). The very rare isotope La is one of the few primordial odd-odd nuclei, with a long half-life of 1.05×10 years: it is one of the proton-rich p-nuclei which cannot be produced in the s- or r-processes. La, along with the even rarer Ta, is produced in the ν-process, where neutrinos interact with stable nuclei. All other lanthanum isotopes are synthetic: with the exception of La with a half-life of about 60,000 years, all of them have half-lives less than a day, and most have half-lives less than a minute. The isotopes La and La occur as fission products of uranium.
Lanthanum oxide is a white solid that can be prepared by direct reaction of its constituent elements. Due to the large size of the La ion, LaO adopts a hexagonal 7-coordinate structure that changes to the 6-coordinate structure of scandium oxide (ScO) and yttrium oxide (YO) at high temperature. When it reacts with water, lanthanum hydroxide is formed: a lot of heat is evolved in the reaction and a hissing sound is heard. Lanthanum hydroxide will react with atmospheric carbon dioxide to form the basic carbonate.

Lanthanum fluoride is insoluble in water and can be used as a qualitative test for the presence of La. The heavier halides are all very soluble deliquescent compounds. The anhydrous halides are produced by direct reaction of their elements, as heating the hydrates causes hydrolysis: for example, heating hydrated LaCl produces LaOCl.

Lanthanum reacts exothermically with hydrogen to produce the dihydride LaH, a black, pyrophoric, brittle, conducting compound with the calcium fluoride structure. This is a non-stoichiometric compound, and further absorption of hydrogen is possible, with a concomitant loss of electrical conductivity, until the more salt-like LaH is reached. Like LaI and LaI, LaH is probably an electride compound.

Due to the large ionic radius and great electropositivity of La, there is not much covalent contribution to its bonding and hence it has a limited coordination chemistry, like yttrium and the other lanthanides. Lanthanum oxalate does not dissolve very much in alkali-metal oxalate solutions, and [La(acac)(HO)] decomposes around 500 °C. Oxygen is the most common donor atom in lanthanum complexes, which are mostly ionic and often have high coordination numbers over 6: 8 is the most characteristic, forming square antiprismatic and dodecadeltahedral structures. These high-coordinate species, reaching up to coordination number 12 with the use of chelating ligands such as in La(SO)·9HO, often have a low degree of symmetry because of stereo-chemical factors.

Lanthanum chemistry tends not to involve π bonding due to the electron configuration of the element: thus its organometallic chemistry is quite limited. The best characterized organolanthanum compounds are the cyclopentadienyl complex La(CH), which is produced by reacting anhydrous LaCl with NaCH in tetrahydrofuran, and its methyl-substituted derivatives.

In 1751, the Swedish mineralogist Axel Fredrik Cronstedt discovered a heavy mineral from the mine at Bastnäs, later named cerite. Thirty years later, the fifteen-year-old Vilhelm Hisinger, from the family owning the mine, sent a sample of it to Carl Scheele, who did not find any new elements within. In 1803, after Hisinger had become an ironmaster, he returned to the mineral with Jöns Jacob Berzelius and isolated a new oxide which they named "ceria" after the dwarf planet Ceres, which had been discovered two years earlier. Ceria was simultaneously independently isolated in Germany by Martin Heinrich Klaproth. Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemist Carl Gustaf Mosander, who lived in the same house as Berzelius: he separated out two other oxides which he named "lanthana" and "didymia". He partially decomposed a sample of cerium nitrate by roasting it in air and then treating the resulting oxide with dilute nitric acid. Since lanthanum's properties differed only slightly from those of cerium, and occurred along with it in its salts, he named it from the Ancient Greek "λανθάνειν" [lanthanein] (lit. "to lie hidden"). Relatively pure lanthanum metal was first isolated in 1923.

Lanthanum is the third-most abundant of all the lanthanides, making up 39 mg/kg of the Earth's crust, behind neodymium at 41.5 mg/kg and cerium at 66.5 mg/kg. It is almost three times as abundant as lead in the Earth's crust. Despite being among the so-called "rare earth metals", lanthanum is thus not rare at all, but it is historically so named because it is rarer than "common earths" such as lime and magnesia, and historically only a few deposits were known. Lanthanum is considered a rare earth metal because the process to mine it is difficult, time-consuming, and expensive. Lanthanum is rarely the dominant lanthanide found in the rare earth minerals, and in their chemical formulae it is usually preceded by cerium. Rare examples of La-dominant minerals are monazite-(La) and lanthanite-(La).
The La ion is similarly-sized to the early lanthanides of the cerium group (those up to samarium and europium) that immediately follow in the periodic table, and hence it tends to occur along with them in phosphate, silicate and carbonate minerals, such as monazite (MPO) and bastnäsite (MCOF), where M refers to all the rare earth metals except scandium and the radioactive promethium (mostly Ce, La, and Y). Bastnäsite is usually lacking in thorium and the heavy lanthanides, and the purification of the light lanthanides from it is less involved. The ore, after being crushed and ground, is first treated with hot concentrated sulfuric acid, evolving carbon dioxide, hydrogen fluoride, and silicon tetrafluoride: the product is then dried and leached with water, leaving the early lanthanide ions, including lanthanum, in solution.

The procedure for monazite, which usually contains all the rare earths as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with sodium hydroxide to pH 3-4. Thorium precipitates out of solution as hydroxide and is removed. After that, the solution is treated with ammonium oxalate to convert rare earths to their insoluble oxalates. The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid that excludes one of the main components, cerium, whose oxide is insoluble in HNO. Lanthanum is separated as a double salt with ammonium nitrate by crystallization. This salt is relatively less soluble than other rare earth double salts and therefore stays in the residue. Care must be taken when handling some of the residues as they contain Ra, the daughter of Th, which is a strong gamma emitter. Lanthanum is relatively easy to extract as it has only one neighbouring lanthanide, cerium, which can be removed by making use of its ability to be oxidised to the +4 state; thereafter, lanthanum may be separated out by the historical method of fractional crystallization of La(NO)·2NHNO·4HO, or by ion-exchange techniques when higher purity is desired.

Lanthanum metal is obtained from its oxide by heating it with ammonium chloride or fluoride and hydrofluoric acid at 300-400 °C to produce the chloride or fluoride:

This is followed by reduction with alkali or alkaline earth metals in vacuum or argon atmosphere:

Also, pure lanthanum can be produced by electrolysis of molten mixture of anhydrous LaCl and NaCl or KCl at elevated temperatures.

The first historical application of lanthanum was in gas lantern mantles. Carl Auer von Welsbach used a mixture of 60% magnesium oxide, 20% lanthanum oxide, and 20% yttrium oxide, which he called "Actinophor" and patented in 1885. The original mantles gave a green-tinted light and were not very successful, and his first company, which established a factory in Atzgersdorf in 1887, failed in 1889.

Modern uses of lanthanum include:

Lanthanum has no known biological role in humans. The element is very poorly absorbed after oral administration and when injected its elimination is very slow. Lanthanum carbonate (Fosrenol) was approved as a phosphate binder to absorb excess phosphate in cases of end stage renal disease.

While lanthanum has pharmacological effects on several receptors and ion channels, its specificity for the GABA receptor is unique among trivalent cations. Lanthanum acts at the same modulatory site on the GABA receptor as zinc, a known negative allosteric modulator. The lanthanum cation La is a positive allosteric modulator at native and recombinant GABA receptors, increasing open channel time and decreasing desensitization in a subunit configuration dependent manner.

Lanthanum is an essential cofactor for the methanol dehydrogenase of the methanotrophic bacterium "Methylacidiphilum fumariolicum" SolV, although the great chemical similarity of the lanthanides means that it may be substituted with cerium, praseodymium, or neodymium without ill effects, and with the smaller samarium, europium, or gadolinium giving no side effects other than slower growth.

Lanthanum has a low to moderate level of toxicity and should be handled with care. The injection of lanthanum solutions produces hyperglycemia, low blood pressure, degeneration of the spleen and hepatic alterations. The application in carbon arc light led to the exposure of people to rare earth element oxides and fluorides, which sometimes led to pneumoconiosis. As the La ion is similar in size to the Ca ion, it is sometimes used as an easily traced substitute for the latter in medical studies. Lanthanum, like the other lanthanides, is known to affect human metabolism, lowering cholesterol levels, blood pressure, appetite, and risk of blood coagulation. When injected into the brain, it acts as a painkiller, similarly to morphine and other opiates, though the mechanism behind this is still unknown.

Lanthanum

Lanthanum compounds have numerous applications as catalysts, additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in lighters and torches, electron cathodes, scintillators, GTAW electrodes, and other things. Lanthanum carbonate is used as a phosphate binder in cases of renal failure. It is also an element in the 6th period and in the 3rd group.

Lanthanum fluoride is insoluble in water and can be used as a qualitative test for the presence of La. The heavier halides are all very soluble deliquescent compounds. The anhydrous halides are produced by direct reaction of their elements, as heating the hydrates causes hydrolysis: for example, heating hydrated LaCl produces LaOCl.

Lanthanum reacts exothermically with hydrogen to produce the dihydride LaH, a black, pyrophoric, brittle, conducting compound with the calcium fluoride structure. This is a non-stoichiometric compound, and further absorption of hydrogen is possible, with a concomitant loss of electrical conductivity, until the more salt-like LaH is reached. Like LaI and LaI, LaH is probably an electride compound.

Lanthanum chemistry tends not to involve π bonding due to the electron configuration of the element: thus its organometallic chemistry is quite limited. The best characterized organolanthanum compounds are the cyclopentadienyl complex La(CH), which is produced by reacting anhydrous LaCl with NaCH in tetrahydrofuran, and its methyl-substituted derivatives.

Lanthanum metal is obtained from its oxide by heating it with ammonium chloride or fluoride and hydrofluoric acid at 300-400 °C to produce the chloride or fluoride:

This is followed by reduction with alkali or alkaline earth metals in vacuum or argon atmosphere:

Also, pure lanthanum can be produced by electrolysis of molten mixture of anhydrous LaCl and NaCl or KCl at elevated temperatures.

The first historical application of lanthanum was in gas lantern mantles. Carl Auer von Welsbach used a mixture of 60% magnesium oxide, 20% lanthanum oxide, and 20% yttrium oxide, which he called "Actinophor" and patented in 1885. The original mantles gave a green-tinted light and were not very successful, and his first company, which established a factory in Atzgersdorf in 1887, failed in 1889.

Modern uses of lanthanum include:

Lanthanum has no known biological role in humans. The element is very poorly absorbed after oral administration and when injected its elimination is very slow. Lanthanum carbonate (Fosrenol) was approved as a phosphate binder to absorb excess phosphate in cases of end stage renal disease.

Lanthanum is an essential cofactor for the methanol dehydrogenase of the methanotrophic bacterium "Methylacidiphilum fumariolicum" SolV, although the great chemical similarity of the lanthanides means that it may be substituted with cerium, praseodymium, or neodymium without ill effects, and with the smaller samarium, europium, or gadolinium giving no side effects other than slower growth.

Several elements were discovered as a consequence of lengthy analysis and decomposition of the ore Gadolinite. As the ore was progressively analysed, the residue was first given the label ceria and then lanthana and then subsequently yttria, erbia, and terbia. In order of date discovered, the list of elements includes Cerium 58, Lanthanum 57, Erbium 68, Terbium 65, Yttrium 39, Ytterbium 70, Holmium 67, Thulium 69, Scandium 21, Praseodymium 59, Neodymium 60 and Dysprosium 66. Several of these new elements were either discovered or isolated by Carl Gustaf Mosander in the 1830s and 1840s.

Lanthanum oxide

Lanthanum oxide, chemical formula LaO, is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock for certain catalysts, among other uses.

Lanthanum oxide is an odorless, white solid that is insoluble in water, but soluble in dilute acid. Depending on the pH of the compound, different crystal structures can be obtained. LaO is hygroscopic; under atmosphere, it absorbs moisture over time and converts to lanthanum hydroxide. Lanthanum oxide has p-type semiconducting properties and a band gap of approximately 5.8 eV.. Its average room temperature resistivity is 10 kΩ·cm, which decreases with an increase in temperature. LaO has the lowest lattice energy of the rare earth oxides, with very high dielectric constant, ε = 27.

At low temperatures, LaO has an A-MO hexagonal crystal structure. The La metal atoms are surrounded by a 7 coordinate group of Oatoms, the oxygen ions are in an octahedral shape around the metal atom and there is one oxygen ion above one of the octahedral faces. On the other hand, at high temperatures the Lanthanum oxide converts to a C-MO cubic crystal structure. The La ion is surrounded by a 6 coordinate group of O ions.

Lanthanum oxide crystallizes as several polymorphs.

To produce hexagonal LaO, a 0.1 M solution of LaCl is sprayed onto a preheated substrate, usually made of metal chalcogenides. The process can be viewed as occurring in two steps – hydrolysis followed by dehydration:

An alternative route to obtaining hexagonal LaO involves precipitation of nominal La(OH) from aqueous solution using a combination of 2.5% NH and the surfactant sodium dodecyl sulfate followed by heating and stirring for 24 hours at 80 °C:

Other routes include:

Lanthanum oxide is used as an additive to develop certain ferroelectric materials, such as La-doped BiTiO (BLT).
Lanthanum oxide is used in optical materials; often the optical glasses are doped with LaO to improve the glass' refractive index, chemical durability, and mechanical strength.

When this 1:3 reaction is mixed into a glass composite, the high molecular weight of the lanthanum causes an increase of the homogeneous mixture of the melt which leads to a lower melting point. The addition of the LaO to the glass melt leads to a higher glass transition temperature from 658 °C to 679 °C. The addition also leads to a higher density, microhardness, and refractive index of the glass.

LaO is used to make optical glasses, to which this oxide confers increased density, refractive index, and hardness. Together with oxides of tungsten, tantalum, and thorium, LaO improves the resistance of the glass to attack by alkali. LaO is an ingredient for the manufacture of piezoelectric and thermoelectric materials. Automobile exhaust-gas converters contain LaO. LaO is also used in X-ray imaging intensifying screens, phosphors as well as dielectric and conductive ceramics. Gives off bright glow.

LaO has been examined for the oxidative coupling of methane.

LaO films can be deposited by many different methods, including chemical vapor disposition, atomic layer deposition, thermal oxidation, sputtering, and spray pyrolysis. Depositions of these films occur in a temperature range of 250–450 °C. Polycrystalline films are formed at 350 °C.

LaO tungsten electrodes are replacing thoriated tungsten electrodes in Gas tungsten arc welding (TIG) due to safety concerns with thorium's radioactivity.

Period 6 element

A period 6 element is one of the chemical elements in the sixth row (or "period") of the periodic table of the elements, including the lanthanides. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The sixth period contains 32 elements, tied for the most with period 7, beginning with caesium and ending with radon. Lead is currently the last stable element; all subsequent elements are radioactive. For bismuth, however, its only primordial isotope, Bi, has a half-life of more than 10 years, over a billion times longer than the current age of the universe. As a rule, period 6 elements fill their 6s shells first, then their 4f, 5d, and 6p shells, in that order; however, there are exceptions, such as gold.

This period contains the lanthanides, also known as the "rare earths". Many lanthanides are known for their magnetic properties, such as neodymium. Many period 6 transition metals are very valuable, such as gold, however many period 6 other metals are incredibly toxic, such as thallium. Period 6 contains the last stable element, lead. All subsequent elements in the periodic table are radioactive. After bismuth, which has a half-life or more than 10 years, polonium, astatine, and radon are some of the shortest-lived and rarest elements known; less than a gram of astatine is estimated to exist on earth at any given time.Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (82 °F), which makes it one of only five elemental metals that are liquid at (or near) room temperature. Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium. The metal is extremely reactive and pyrophoric, reacting with water even at−116 °C (−177 °F). It is the least electronegative element having a stable isotope, caesium-133. Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors.

Two German chemists, Robert Bunsen and Gustav Kirchhoff, discovered caesium in 1860 by the newly developed method of flame spectroscopy. The first small-scale applications for caesium have been as a "getter" in vacuum tubes and in photoelectric cells. In 1967, a specific frequency from the emission spectrum of caesium-133 was chosen to be used in the definition of the second by the International System of Units. Since then, caesium has been widely used in atomic clocks.

Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids. It has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. Although the element is only mildly toxic, it is a hazardous material as a metal and its radioisotopes present a high health risk in case of radioactivity releases.

Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with water and carbon dioxide and is not found as a mineral. The most common naturally occurring minerals are the very insoluble barium sulfate, BaSO (barite), and barium carbonate, BaCO(witherite). Barium's name originates from Greek "barys" (βαρύς), meaning "heavy", describing the high density of some common barium-containing ores.

Barium has few industrial applications, but the metal has been historically used to scavenge air in vacuum tubes. Barium compounds impart a green color to flames and have been used in fireworks. Barium sulfate is used for its density, insolubility, and X-ray opacity. It is used as an insoluble heavy additive to oil well drilling mud, and in purer form, as an X-ray radiocontrast agent for imaging the human gastrointestinal tract. Soluble barium compounds are poisonous due to release of the soluble barium ion, and have been used as rodenticides. New uses for barium continue to be sought. It is a component of some "high temperature" YBCOsuperconductors, and electroceramics.

The lanthanide or lanthanoid (IUPAC nomenclature) series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium. These fifteen elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements.

The informal chemical symbol Ln is used in general discussions of lanthanide chemistry. All but one of the lanthanides are f-block elements, corresponding to the filling of the 4f electron shell; lanthanum, a d-block element, is also generally considered to be a lanthanide due to its chemical similarities with the other fourteen. All lanthanide elements form trivalent cations, Ln, whose chemistry is largely determined by the ionic radius, which decreases steadily from lanthanum to lutetium.

The lanthanide elements are the group of elements with atomic number increasing from 57 (lanthanum) to 71 (lutetium). They are termed lanthanide because the lighter elements in the series are chemically similar to lanthanum. Strictly speaking, both lanthanum and lutetium have been labeled as group 3 elements, because they both have a single valence electron in the d shell. However, both elements are often included in any general discussion of the chemistry of the lanthanide elements.

In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods).

Lanthanum is a chemical element with the symbol La and atomic number 57. It is the first element in the lanthanide series. It is a soft, ductile, silvery-white metal that tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. It is also sometimes considered the first element of the 6th-period transition metals and is traditionally counted among the rare earth elements. The usual oxidation state is +3. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.

Lanthanum compounds have numerous applications as catalysts, additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in lighters and torches, electron cathodes, scintillators, GTAW electrodes, and other things. Lanthanum carbonate is used as a phosphate binder in cases of renal failure. It is also an element in the 6th period and in the 4th group.

Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869. Hafnium was the penultimate stable isotope element to be discovered (rhenium was identified two years later). Hafnium is named for "Hafnia", the Latin name for "Copenhagen", where it was discovered.

Hafnium is used in filaments and electrodes. Some semiconductor fabrication processes use its oxide for integrated circuits at 45 nm and smaller feature lengths. Some superalloys used for special applications contain hafnium in combination with niobium, titanium, or tungsten.

Hafnium's large neutron capture cross-section makes it a good material for neutron absorption in control rods in nuclear power plants, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors.

Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as "tantalium", the name comes from "Tantalus", a character from Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory metals group, which are widely used as minor component in alloys. The chemical inertness of tantalum makes it a valuable substance for laboratory equipment and a substitute for platinum, but its main use today is in tantalum capacitors in electronic equipment such as mobile phones, DVD players, video game systems and computers.
Tantalum, always together with the chemically similar niobium, occurs in the minerals tantalite, columbite and coltan (a mix of columbite and tantalite).

Tungsten, also known as wolfram, is a chemical element with the chemical symbol W and atomic number 74. The word "tungsten" comes from the Swedish language "tung sten" directly translatable to "heavy stone", though the name is "volfram" in Swedish to distinguish it from Scheelite, in Swedish alternatively named "tungsten".

A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as a metal in 1783. Its important ores include wolframite and scheelite. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the non-alloyed metals and the second highest of all the elements after carbon. Also remarkable is its high density of 19.3 times that of water, comparable to that of uranium and gold, and much higher (about 1.7 times) than that of lead. Tungsten with minor amounts of impurities is often brittle and hard, making it difficult to work. However, very pure tungsten, though still hard, is more ductile, and can be cut with a hard-steel hacksaw.

The unalloyed elemental form is used mainly in electrical applications. Tungsten's many alloys have numerous applications, most notably in incandescent light bulb filaments, X-ray tubes (as both the filament and target), electrodes in TIG welding, and superalloys. Tungsten's hardness and high density give it military applications in penetrating projectiles. Tungsten compounds are most often used industrially as catalysts.

Tungsten is the only metal from the third transition series that is known to occur in biomolecules, where it is used in a few species of bacteria. It is the heaviest element known to be used by any living organism. Tungsten interferes with molybdenum and copper metabolism, and is somewhat toxic to animal life.

Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an "estimated" average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust. The free element has the third-highest melting point and highest boiling point of any element. Rhenium resembles manganese chemically and is obtained as a by-product of molybdenum and copper ore's extraction and refinement. Rhenium shows in its compounds a wide variety of oxidation states ranging from −1 to +7.

Discovered in 1925, rhenium was the last stable element to be discovered. It was named after the river Rhine in Europe.

Nickel-based superalloys of rhenium are used in the combustion chambers, turbine blades, and exhaust nozzles of jet engines, these alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element, with the chemical industry's catalytic uses being next-most important. Because of the low availability relative to demand, rhenium is among the most expensive of metals, with an average price of approximately US$4,575 per kilogram (US$142.30 per troy ounce) as of August 2011; it is also of critical strategic military importance, for its use in high performance military jet and rocket engines.

Osmium is a chemical element with the symbol Os and atomic number 76. It is a hard, brittle, blue-gray or blue-black transition metal in the platinum family and is the densest naturally occurring element, with a density of (slightly greater than that of iridium and twice that of lead). It is found in nature as an alloy, mostly in platinum ores; its alloys with platinum, iridium, and other platinum group metals are employed in fountain pen tips, electrical contacts, and other applications where extreme durability and hardness are needed.

Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element (after osmium) and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Although only certain molten salts and halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can be flammable.

Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named the iridium for the goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts. Iridium is one of the rarest elements in the Earth's crust, with annual production and consumption of only three tonnes. and are the only two naturally occurring isotopes of iridium as well as the only stable isotopes; the latter is the more abundant of the two.

The most important iridium compounds in use are the salts and acids it forms with chlorine, though iridium also forms a number of organometallic compounds used in industrial catalysis, and in research. Iridium metal is employed when high corrosion resistance at high temperatures is needed, as in high-end spark plugs, crucibles for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the chloralkali process. Iridium radioisotopes are used in some radioisotope thermoelectric generators.

Iridium is found in meteorites with an abundance much higher than its average abundance in the Earth's crust. For this reason the unusually high abundance of iridium in the clay layer at the Cretaceous–Paleogene boundary gave rise to the Alvarez hypothesis that the impact of a massive extraterrestrial object caused the extinction of dinosaurs and many other species 66 million years ago. It is thought that the total amount of iridium in the planet Earth is much higher than that observed in crustal rocks, but as with other platinum group metals, the high density and tendency of iridium to bond with iron caused most iridium to descend below the crust when the planet was young and still molten.

Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78.

Its name is derived from the Spanish term "platina", which is literally translated into "little silver". It is a dense, malleable, ductile, precious, gray-white transition metal.

Platinum has six naturally occurring isotopes. It is one of the rarest elements in the Earth's crust and has an average abundance of approximately 5 μg/kg. It is the least reactive metal. It occurs in some nickel and copper ores along with some native deposits, mostly in South Africa, which accounts for 80% of the world production.

As a member of the platinum group of elements, as well as of the group 10 of the periodic table of elements, platinum is generally non-reactive. It exhibits a remarkable resistance to corrosion, even at high temperatures, and as such is considered a noble metal. As a result, platinum is often found chemically uncombined as native platinum. Because it occurs naturally in the alluvial sands of various rivers, it was first used by pre-Columbian South American natives to produce artifacts. It was referenced in European writings as early as 16th century, but it was not until Antonio de Ulloa published a report on a new metal of Colombian origin in 1748 that it became investigated by scientists.

Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum-resistance thermometers, dentistry equipment, and jewelry. Because only a few hundred tonnes are produced annually, it is a scarce material, and is highly valuable and is a major precious metal commodity. Being a heavy metal, it leads to health issues upon exposure to its salts, but due to its corrosion resistance, it is not as toxic as some metals. Its compounds, most notably cisplatin, are applied in chemotherapy against certain types of cancer.

Gold is a dense, soft, shiny, malleable and ductile metal. It is a chemical element with the symbol Au and atomic number 79.

Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements solid under standard conditions. The metal therefore occurs often in free elemental (native) form, as nuggets or grains in rocks, in veins and in alluvial deposits. Less commonly, it occurs in minerals as gold compounds, usually with tellurium.

Gold resists attacks by individual acids, but it can be dissolved by the aqua regia (nitro-hydrochloric acid), so named because it dissolves gold. Gold also dissolves in alkaline solutions of cyanide, which have been used in mining. Gold dissolves in mercury, forming amalgam alloys. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to confirm the presence of gold in items, giving rise to the term "the acid test."

Gold has been a valuable and highly sought-after precious metal for coinage, jewelry, and other arts since long before the beginning of recorded history. Gold standards have been a common basis for monetary policies throughout human history, later being supplanted by fiat currency starting in the 1930s. The last gold certificate and gold coin currencies were issued in the U.S. in 1932. In Europe, most countries left the gold standard with the start of World War I in 1914 and, with huge war debts, failed to return to gold as a medium of exchange.

A total of 165,000 tonnes of gold have been mined in human history, as of 2009. This is roughly equivalent to 5.3 billion troy ounces or, in terms of volume, about 8500 m, or a cube 20.4 m on a side. The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.

Besides its widespread monetary and symbolic functions, gold has many practical uses in dentistry, electronics, and other fields. Its high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity led to many uses of gold, including electric wiring, colored-glass production and even gold leaf eating.

It has been claimed that most of the Earth's gold lies at its core, the metal's high density having made it sink there in the planet's youth. Virtually all of the gold that mankind has discovered is considered to have been deposited later by meteorites which contained the element. This supposedly explains why, in prehistory, gold appeared as nuggets on the earth's surface.

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum ( < Greek "" "water" and "" "silver"). A heavy, silvery d-block element, mercury is the only metal that is liquid at standard conditions for temperature and pressure; the only other element that is liquid under these conditions is bromine, though metals such as caesium, francium, gallium, and rubidium melt just above room temperature. With a freezing point of −38.83 °C and boiling point of 356.73 °C, mercury has one of the narrowest ranges of its liquid state of any metal.

Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). The red pigment vermilion is mostly obtained by reduction from cinnabar. Cinnabar is highly toxic by ingestion or inhalation of the dust. Mercury poisoning can also result from exposure to water-soluble forms of mercury (such as mercuric chloride or methylmercury), inhalation of mercury vapor, or eating seafood contaminated with mercury.

Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, mercury switches, and other devices though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical environments in favor of alcohol-filled, galinstan-filled, digital, or thermistor-based instruments. It remains in use in scientific research applications and in amalgam material for dental restoration. It is used in lighting: electricity passed through mercury vapor in a phosphor tube produces short-wave ultraviolet light which then causes the phosphor to fluoresce, making visible light.

Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray other metal resembles tin but discolors when exposed to air. The two chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861 by the newly developed method of flame spectroscopy. Both discovered the new element in residues of sulfuric acid production.

Approximately 60–70% of thallium production is used in the electronics industry, and the remainder is used in the pharmaceutical industry and in glass manufacturing. It is also used in infrared detectors. Thallium is highly toxic and was used in rat poisons and insecticides. Its use has been reduced or eliminated in many countries because of its nonselective toxicity. Because of its use for murder, thallium has gained the nicknames "The Poisoner's Poison" and "Inheritance Powder" (alongside arsenic).

Lead is a main-group element in the carbon group with the symbol Pb (from ) and atomic number 82. Lead is a soft, malleable other metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a liquid.

Lead is used in building construction, lead-acid batteries, bullets and shots, weights, as part of solders, pewters, fusible alloys and as a radiation shield. Lead has the highest atomic number of all of the stable elements, although the next higher element, bismuth, has a half-life that is so long (much longer than the age of the universe) that it can be considered stable. Its four stable isotopes have 82 protons, a magic number in the nuclear shell model of atomic nuclei.

Lead, at certain exposure levels, is a poisonous substance to animals as well as for human beings. It damages the nervous system and causes brain disorders. Excessive lead also causes blood disorders in mammals. Like the element mercury, another heavy metal, lead is a neurotoxin that accumulates both in soft tissues and the bones. Lead poisoning has been documented from ancient Rome, ancient Greece, and ancient China.

Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent other metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead. It is a brittle metal with a silvery white color when newly made, but often seen in air with a pink tinge owing to the surface oxide. Bismuth metal has been known from ancient times, although until the 18th century it was often confused with lead and tin, which each have some of the metal's bulk physical properties. The etymology is uncertain but possibly comes from Arabic "bi ismid" meaning having the properties of antimony or German words "weisse masse" or "wismuth" meaning"white mass."

Bismuth is the most naturally diamagnetic of all metals, and only mercury has a lower thermal conductivity.

Bismuth has classically been considered to be the heaviest naturally occurring stable element, in terms of atomic mass. Recently, however, it has been found to be very slightly radioactive: its only primordial isotope bismuth-209 decays via alpha decay into thallium-205 with a half-life of more than a billion times the estimated age of the universe.

Bismuth compounds (accounting for about half the production of bismuth) are used in cosmetics, pigments, and a few pharmaceuticals. Bismuth has unusually low toxicity for a heavy metal. As the toxicity of lead has become more apparent in recent years, alloy uses for bismuth metal (presently about a third of bismuth production), as a replacement for lead, have become an increasing part of bismuth's commercial importance.

Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uraniumores. Polonium has been studied for possible use in heating spacecraft. As it is unstable, all isotopes of polonium are radioactive. There is disagreement as to whether polonium is a post-transition metal or metalloid.

Astatine is a radioactive chemical element with the symbol At and atomic number 85. It occurs on the Earth only as the result of decay of heavier elements, and decays away rapidly, so much less is known about this element than its upper neighbors in the periodic table. Earlier studies have shown this element follows periodic trends, being the heaviest known halogen, with melting and boiling points being higher than those of lighter halogens.

Until recently most of the chemical characteristics of astatine were inferred from comparison with other elements; however, important studies have already been done. The main difference between astatine and iodine is that the HAt molecule is chemically a hydride rather than a halide; however, in a fashion similar to the lighter halogens, it is known to form ionic astatides with metals. Bonds to nonmetals result in positive oxidation states, with +1 best portrayed by monohalides and their derivatives, while the higher are characterized by bond to oxygen and carbon. Attempts to synthesize astatine fluoride have been met with failure. The second longest-living astatine-211 is the only one to find a commercial use, being useful as an alpha emitter in medicine; however, only extremely small quantities are used, and in larger ones it is very hazardous, as it is intensely radioactive.

Astatine was first produced by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè in the University of California, Berkeley in 1940. Three years later, it was found in nature; however, with an estimated amount of less than 28 grams (1 oz) at given time, astatine is the least abundant element in Earth's crust among non-transuranium elements. Among astatine isotopes, six (with mass numbers 214 to 219) are present in nature as the result of decay of heavier elements; however, the most stable astatine-210 and the industrially used astatine-211 are not.

Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, Rn, has a half-life of 3.8 days. Radon is one of the densest substances that remains a gas under normal conditions. It is also the only gas that is radioactive under normal conditions, and is considered a health hazard due to its radioactivity. Intense radioactivity also hindered chemical studies of radon and only a few compounds are known.

Radon is formed as part of the normal radioactive decay chain of uranium and thorium. Uranium and thorium have been around since the earth was formed and their most common isotope has a very long half-life (14.05 billion years). Uranium and thorium, radium, and thus radon, will continue to occur for millions of years at about the same concentrations as they do now. As the radioactive gas of radon decays, it produces new radioactive elements called radon daughters or decay products. Radon daughters are solids and stick to surfaces such as dust particles in the air. If contaminated dust is inhaled, these particles can stick to the airways of the lung and increase the risk of developing lung cancer.

Radon is responsible for the majority of the public exposure to ionizing radiation. It is often the single largest contributor to an individual's background radiation dose, and is the most variable from location to location. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as attics and basements. It can also be found in some spring waters and hot springs.

Epidemiological studies have shown a clear link between breathing high concentrations of radon and incidence of lung cancer. Thus, radon is considered a significant contaminant that affects indoor air quality worldwide. According to the United States Environmental Protection Agency, radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States. About 2,900 of these deaths occur among people who have never smoked. While radon is the second most frequent cause of lung cancer, it is the number one cause among non-smokers, according to EPA estimates.

Of the period 6 elements, only tungsten is known to have any biological role in organisms. However, gold, platinum, mercury, and some lanthanides such as gadolinium have applications as drugs.

Most of the period 6 elements are toxic(for instance lead) and produce heavy-element poisoning. Promethium, polonium, astatine and radon are radioactive, and therefore present radioactive hazards.

Mosander worked teaching chemistry at the Institute and as an assistant in the mineralogical collection of the Swedish Museum of Natural History. In 1836 he succeeded his professor of chemistry during his medical studies, Jöns Jakob Berzelius, as professor of chemistry and pharmacy in the Karolinska Institute. Mosander discovered lanthanum in 1839 when he partially decomposed a sample of cerium nitrate by heating and treating the resulting salt with dilute nitric acid. In 1843 he discovered terbium and erbium.

Carl Gustaf Mosander

Carl Gustaf Mosander (10 September 1797 – 15 October 1858) was a Swedish chemist. He discovered the elements lanthanum, erbium and terbium.

Born in Kalmar, Mosander attended school there until he moved to Stockholm with his mother at age 12. In Stockholm, he became an apprentice at the "Ugglan" pharmacy. He took his pharmacy examination in 1817, but had an interest in medicine and matriculated as a student in the Karolinska Institute in 1820 and graduated with his Master of Surgery degree in 1824.

Mosander was elected a member of the Royal Swedish Academy of Sciences in 1833.

He died in Lovön, Stockholm County, at age 61.