Rubidium, cesium, and francium

Rubidium is widely distributed in the earth's crust, being more abundant overall than lead, copper, or zinc. However, it appears in such small amounts that its production is limited. It is most often used industrially as a catalyst to speed up chemical reactions. It is also used in making photocells and vacuum tubes.

Cesium is widely distributed in low concen­trations in brines and mineral waters. It is used as the time-measuring element in atomic clocks. Scientists are also studying the possi­bilities of using cesium in the generation of power and as a fuel for space vehicles.

Francium has more than 20 isotopes, all of which are short-lived and radioactive. No weighable amount of the element has even been extracted, and at any one time there is only about 25 grams of it throughout the whole of the earth's crust.

Sodium vaporis used in some streetlights because the orange light emitted when an electric current passes through the vapor is very intense. It also pene­trates mist and fog better than does white light.

Many types of preserved meats—most sausages, for example—contain potas­sium nitrate. This com­pound inhibits the growth of harmful microorganisms such as Salmonella, which causes food poisoning.

Fact entries

Lithiumwas discovered in 1817 by the Swedish chem­ist lohann Arfvedson (1792-1841). Its name derives from the Creek lithos, meaning stone. At. no. 3; at. mass 6.941; m.p. 180.54° C;b.p. 1347° C.

Sodiumwas discovered in 1807 by the British scientist Humphry Davy (1778-1827). He named it after the alka­line substance soda. At. no.

11; at. mass 22.9898; m.p. 97.8° C; b.p. 881° C. The sym­bol for sodium, Na, comes from its Latin name natrium.

Potassiumwas isolated by Humphry Davy in 1807. It was originally called kalium, the Latinized form of the Ar­abic word for alkali. At. no. 19; at. mass 39.0983; m.p. 63.2° C; b.p. 766° C.

Rubidiumwas discovered

in 1861 by the German chemists Robert Bunsen (1811-1899) and Gustav Kirchhoff (1824-1887). It is so named because of the dom­inant red lines in its spec­trum. The Latin rubidus means red. At. no. 37; at. mass 85.4678; m.p. 38.84° C; b.p. 688° C.

Cesiumwas discovered in 1860 by Robert Bunsen and Gustav Kirchhoff. It was

named after the characteris­tic blue lines in its spec­trum. At. no. 55; at. mass 132.905; m.p. 28.4° C; b.p. 678.4° C.

Franciumwas discovered in 1939 by the French chem­ist Marguerite Perey (1900-1975). She named it after her homeland. At. no. 87. Little else is known about the ele­ment because no stable iso­topes exist. There is one nat-

ural isotope, which is the longest-lived (half-life 21 minutes).

Date: 2015-12-11; view: 1885