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The X-ray photograph

shows a human stomach. It is visible only because the patient has swallowed a "barium meal." This sub­stance contains barium sul­fate, a substance that is opaque to X rays.


 


Fact entries

Berylliumwas discovered in the silicon-containing mineral beryl (from which its name derives) in 1798 by the French chemist Louis Vauquelin (1763-1829). The free metal was first isolated in 1828 by the German chemist Fredrich Wohler (1800-1882) and, independ­ently, by the French chemist Antoine Bussy (1794-1882). At. no. 4; at. mass 9.0128; m.p. 1278+5° C;b.p. 2970° C.

Magnesiumwas first iso­lated as the free metal in 1808 by the British scientist Humphry Davy (1778-1827), although its compounds (for


example, Epsom salts and magnesia) were known much earlier. The element is named after the ancient Creek region of Magnesia. At. no. 12; at. mass 24.305; m.p. 650° C; b.p. 1110+10° C.

Calciumwas first isolated as the free metal in 1808 by Humphry Davy. Its name is derived from the Latin calx, meaning lime—a calcium compound known since an­cient times. At. no. 20; at. mass 40.08; m.p. 839° C; b.p. 1484° C.

Strontiumwas first found at Strontian (hence, the ele-


ment's name) in Scotland in 1790 by the British scientist Adair Crawford. The metal itself was isolated in 1808 by Humphry Davy. At. no. 38; at. mass 87.62; m.p. 769° C; b.p. 1384°C.

Bariumderives its name from the Greek barys— meaning heavy—although the metal is not particularly dense. It was first detected in 1774 by the Swedish chemist Karl Scheele (1742-1786). The free metal was isolated in 1808 by Hum­phry Davy. At. no. 56; at. mass 137.33; m.p. about 725° C; b.p. about 1140° C.


Radiumwas discovered in the radioactive mineral pitchblende (a uranium ore) in 1898 by the French scien­tist Pierre Curie (1859-1906) and his Polish-born wife Marie (1867-1934). The metal itself was isolated in 1910 by Marie Curie. Its name is de­rived from the Latin radius, meaning ray. At. no. 88; at. mass 226.025; m.p. about 700° C; b.p. about 1140° C; half-life (of stablest isotope) 1,600 years.


 
 

These three metals are classed together as Group 2B of the periodic table. At first glance, they appear to be dissimilar. Zinc (Zn) is a soft metal. Cadmium (Cd) and its compounds are poisonous. Mercury (Hg) is the only metallic element that is liquid at ordinary tempera­tures. Chemically, however, these metals be­have alike. They all react with oxygen to form various compounds. Zinc Zinc is a shiny, bluish-white metal that is hard and brittle at room temperature. Zinc was first smelted in China and India, in about 1000 A.D. The technology for making zinc appeared in the West in the eighteenth century when the metal was called Indian tin or calamine. Zinc is comparatively rare in nature, although widely distributed, occurring mainly in combination with sulfur in a mineral called sphalerite, or

 

 



    B 10.81
 
    Al
IB 2B 26.9815
Cu Zn Ga
63.546 65.39 69.72
Ag Cd In
107.868 112.41 114.82
Au Hg Tl
196.967 200 59 204.383

Zinc, cadmium, and mer-curyconstitute Group 2B of the periodic table. They are chemically similar to each other. However, they are physically dissimilar.

The suspended steel pipes/right/ have just been galvanized. This means they have just been coated with a layer of zinc by being dipped into a bath of the molten metal. The zinc coat­ing on galvanized steel pre­vents the steel from rusting. The zinc itself does not cor­rode easily because, in air, a thin film of zinc oxide forms on its surface. This protects the underlying metal.



Date: 2015-12-11; view: 191


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