Kaplan MCAT General Chemistry Review

Eventually, fascination with theories of uric acid wore off, and lithium’s time in the spotlight seemed to be coming to an end. Then, in the 1940s, doctors began to recommend salt-restricted diets for cardiac patients. Lithium chloride was made commercially available as a salt (sodium chloride) substitute. Unfortunately, lithium is quite toxic at fairly low concentrations, and when medical literature in the late 1940s reported several incidents of severe poisonings and multiple deaths—some associated with only minor lithium overdosing—U.S. companies voluntarily withdrew all lithium salts from the market. Right around this time, Australian psychiatrist John Cade proposed the use of lithium salts for the treatment of mania. Cade’s clinical trials were quite successful. In fact, his use of lithium salts to control mania was the first instance of successful medical treatment of a mental illness—and lithium carbonate became commonly prescribed in Europe for manic behavior. Not until 1970 did the U.S. Food and Drug Administration finally approve the use of lithium carbonate for manic illnesses.

Lithium (Li) is a chemical element with atomic number 3. It is an alkali metal, very soft, and under standard conditions it is the least-dense solid element, with a specific gravity of 0.53. Lithium is so reactive that it does not naturally occur on earth in its elemental form, being found only in various salt compounds.

Why would medical scientists pay attention to this particular element? What would make medical scientists believe that lithium chloride would be a good substitute for sodium chloride for patients on salt-restricted diets? The answers lie in the periodic table.

The Periodic Table

In 1869, Russian chemist Dmitri Mendeleev published the first version of his periodic table, in which he showed that ordering the known elements according to atomic weight produced a pattern of periodically recurring physical and chemical properties. Since then, the periodic table of the elements has been revised, using the work of physicist Henry Moseley, to organize the elements on the basis of increasing atomic number rather than atomic weight. Using this revised table, the properties of certain elements that had not yet been discovered were predicted. Experimentation later confirmed a number of these predictions. The periodic table puts into visual representation the principle of the periodic law: The chemical and physical properties of the elements are dependent, in a periodic way, upon their atomic numbers.

The modern periodic table arranges the elements into periods (rows) and groups (columns), also known as families. There are seven periods, representing the principal quantum numbers n = 1 through n = 7. Each period is filled sequentially, and each element in a given period has one more proton and one more electron (in the neutral state) than the element to its left. Groups or families include elements that have the same electronic configuration in their valence shell, which is the outermost shell, and share similar chemical properties. The electrons in the valence shell, known as the valence electrons, are the farthest from the nucleus and have the greatest amount of potential energy of all the electrons in the atom. Their higher potential energy and the fact that they are held less tightly by the nucleus allows them to become involved in chemical bonds with other elements (by way of the valence shells of the other elements); the valence shell electrons largely determine the chemical reactivity and properties of the element.