62 | The History and Use of Our Earth’s Chemical Elements Cesium is used as a hydrogenation catalyst to enhance and assist the reaction in the con-

62 | The History and Use of Our Earth’s Chemical Elements Cesium is used as a hydrogenation catalyst to enhance and assist the reaction in the con-

version of liquid oils to solids forms (e.g., in the production of margarine).

In a molten state, it is used as a heat-transfer fluid in plants generating electric power. Cesium is used experimentally as a plasma to produce a source of ions to power outer space

vehicles using ion engines. Cesium is used in military infrared devices and signal lamps as well as in other optical devices.

Cesium is used as a chemical reagent and reducing agent in industry and the laboratory. It can also be used as an antidote for arsenic poisoning.

Examples฀of฀Compounds Cesium bromide (CsBr) crystals are used in scintillation counters to detect radiation. The

compound is also used to coat the inside of fluorescent screens. Cesium carbonate (Cs 2 CO 3 ) is used in the beer-brewing industry to make the “head” of beer foamier. It is also used in glassmaking and to enhance the taste of mineral water. Cesium chloride (CsCl) is produced by the reaction of cesium metal with chlorine gas (Ca + + Cl - → CsCl). It is also used in the beer brewing industry, to coat fluorescent screens, and to improve the taste of mineral water.

Cesium hydroxide (CsOH) is the strongest base (alkali) with the highest pH value of any chemical yet found. It is easy to produce by just placing cesium metal in water (which is very reactive). After the hydrogen escapes, cesium hydroxide remains in the water (2Cs + H 2 → 2CsOH + H 2 ). Cesium-137 is a highly useful radioisotope that emits its radiation at a very steady and controllable rate. This makes it useful as an atomic clock because it is extremely accurate and never needs winding or a new battery. It is also useful as a radiation source for treatment of malignant cancers. Cs-137 has replaced the much more dangerous cobalt-60 as a source of radiation in industry and medicine.

Hazards Although cesium has many of the properties and characteristics of the other alkali met-

als, because of the large size of its atoms, cesium metal is much more reactive and dangerous to handle. Special precautions need to be taken to keep it away from air, water, and organic substances with which it can vigorously react. Its use should be restricted to laboratories and industries capable of using it safely.

Cesium-137, with a half-life of about 30 years, produces dangerous radiation and can cause radiation poisoning if mishandled. It is used to sterilize wheat, potatoes, and other foods to protect them from insect damage and rotting. It is also used to kill bacteria in the treatment of sewage sludge.

FRANCIUM SYMBOL:฀Fr฀ PERIOD:฀7฀ GROUP:฀1฀(IA)฀ ATOMIC฀NO:฀87

ATOMIC฀MASS:฀223฀amu฀ VALENCE:฀1฀ OXIDATION฀STATE:฀+1฀(?).฀฀NATURAL฀STATE:฀

Solid,฀unstable,฀radioactive.

Guide to the Elements | 63

ORIGIN฀OF฀NAME:฀In฀1939฀Marguerite฀Perey฀(1909–1975),฀a฀French฀physicist฀who฀ worked฀for฀the฀Curie฀institute฀in฀Paris,฀named฀the฀newly฀discovered฀element฀after฀her฀ country—France.

ISOTOPES:฀There฀are฀no฀stable฀isotopes฀of฀francium฀found฀on฀Earth.฀All฀of฀its฀33฀isotopes฀ (ranging฀from฀Fr-201฀to฀Fr-232)฀are฀radioactive;฀therefore,฀the฀one฀with฀the฀longest฀half- life฀of฀about฀20฀minutes฀(Fr-223)฀is฀the฀one฀used฀to฀determine฀its฀atomic฀weight.฀Fr-223฀ is฀the฀only฀radioisotope฀of฀francium฀that฀is฀found฀naturally฀as฀a฀decay฀product฀from฀other฀ unstable฀elements.

ELECTRON฀CONFIGURATION ฀ Energy฀Levels/Shells/Electrons฀ Orbitals/Electrons

s2,฀p6

฀ 3-M฀=฀18฀

s2,฀p6,฀d10

฀ 4-N฀=฀32฀

s2,฀p6,฀d10,฀f14

฀ 5-O฀=฀18฀

s2,฀p6,฀d10

฀ 6-P฀=฀8฀

s2,฀p6

฀ 7-Q฀=฀1฀