Isotopes of hydrogen

There are three isotopes, or forms, of hydro­gen. Protium, the most common one, has a sin­gle proton in its nucleus. Deuterium, or heavy hydrogen, has one proton and one neutron in its nucleus. Tritium, the third isotope, has one proton and two neutrons.

Heavy water is a compound of deuterium and oxygen. It is used in some nuclear reac­tors to help control the nuclear reactions. Tri­tium is radioactive and has been used in com­bination with deuterium in the hydrogen bomb. Scientists are currently working for greater control of the type of reaction that oc­curs when a hydrogen bomb explodes. If these reactions could be controlled, then the deuterium of heavy water could be a virtually unlimited source of energy.

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The Hindenburg, a

hydrogen-filled airship 80 4 feet (245 meters) long, burst into flames on approaching the mooring mast at Lake-hurst, New Jersey, on May 6,1937. As a result of this still unexplained disaster, interest in airships waned. Recently, however, it has re­vived and several experi­mental airships have been built. These modern craft are filled with helium, which is not inflammable.

Liquid hydrogenhas been used as a propellant for sev­eral spacecraft. These have included the second and third stages of the Saturn V rocket, used to launch the historic Apollo 11 mission that landed the first men on the Moon. In such propul­sion systems, the liquid hy­drogen is reacted with liq­uid oxygen, producing water (in the form of steam)—and a powerful thrust.

Fact entries

Hydrogenwas first distin­guished from other inflam­mable gases in 1766 by the British chemist Henry Cav­endish (1731-1810). The for­mation of water by burning the gas was observed in 1776. The name hydrogen (from the Creek hydro and genes, meaning "water former") was proposed in

1781 by the French chemist Antoine Lavoisier (1743-1794). At. no. 1; at. mass 1.0079; m.p. -257.87° C; b.p. — 259.14° C. Isotopes: pro­tium (relative abundance 99.98%), deuterium, tritium.

Deuteriumwas discovered in 1932 by the American physicist Harold Urey (1893-1981). At. no. l;at. mass 2.01410; m.p. -254.4° C; b.p. — 249.5° C; relative abun­dance 0.0149%; made by electrolysis of heavy water.

Tritiumwas discovered in 1934 by the British physicist Ernest Rutherford (1871-1937) and the Australian physicist Marcus Oliphant (1901- ).At. no. 1;at. mass 3.022; m.p. —252.5° C; b.p. -248.1° C; relative abundance less than .005%; radioactive (half-life 12.26 years).

The alkali metalsconsti­tute Group 1A of the peri­odic table. In general, each alkali metal element is more reactive than its counterpart in the neighboring Group 2A.

Alkali metals

The six elements of Group 1A of the periodic table are known as the alkali metals. They are lithium (Li), sodium (Na), potassium (K), rubid­ium (Rb), cesium (Cs), and francium (Fr). All ex­cept lithium are highly reactive chemically. They burn in air and react vigorously—some­times explosively—with water to form strongly alkaline hydroxides. These are compounds containing the positive ion of an alkali metal and the negative ion of a hydroxide molecule (hydrogen and oxygen).

Because of their reactivity, the free metals (except lithium) are normally stored out of con­tact with air, usually under a layer of hydrocar­bon oil. Sodium and potassium occur widely in nature as salts and are essential for many forms of life, whereas francium, on the other hand, is one of the rarest naturally occurring elements. Sodium and potassium have by far the most industrial importance of all the alkali metals.

All six alkali metals, with the exception of francium, are light and silvery white. They are soft enough to be cut with a knife.

Lithium

The first member of the series, lithium, is the lightest known metal, being only half as heavy as an equal volume of water. Lithium is found only in combination with other elements, its usual source being spodumene. This is a com­pound composed of lithium, aluminum, and silicon, containing about 3.7 per cent lithium. Lithium, like sodium, reacts with water to re­lease hydrogen gas. Unlike sodium, however, the reaction does not set the hydrogen on fire. There are many uses for lithium. Being very light, it is used in various alloys, notably with copper, helping to strengthen the alloy with-

out adding too much weight. Lithium is used in the manufacture of certain types of batter­ies, enamels, glass, and ceramic products. Lith­ium soaps are used in lubricating greases em­ployed at high temperatures. Lithium compounds are used in rubber products and in dyes for textiles. One compound, lithium carbonate, is a drug used in the treatment of some types of mental disorders.

Sodium and Potassium

Sodium is the sixth most abundant element, making up about 2.8 per cent of the earth's crust. It occurs in nature mainly as sodium chloride—common table salt—a major compo­nent of seawater.

In some tropical countries, evaporation of seawater under the heat of the sun has been used for many centuries as a production method. In other parts of the world, under­ground salt domes (mines) are the principal source of salt. Other natural sources of so­dium include soda ash and borax.

Much of the sodium chloride produced is converted to sodium hydroxide (caustic soda) and chlorine, both of which have many indus­trial applications. Different sodium salts are used in the manufacture of glass and some ce­ramics. Other salts are used in household de­tergents, weedkillers, photographic chemi­cals, and in tanning leather. Metallic sodium is used as a coolant in some nuclear reactors.

In higher animals, a certain amount of so­dium as well as potassium are necessary to maintain a normal flow of water between the body fluids and the cells. Sodium and potas­sium are also essential for tissue formation, muscle contraction, and changing food into energy.

Potassium is also an abundant element, but occurs mainly in rocks and clays and is diffi­cult to extract. It makes up about 2.5 per cent of the earth's crust. Seawater contains potas-

Date: 2015-12-11; view: 1702