Document 91vrbDx6jxRBJNEMQDV4ednme

by Donald H. Andrews B. N. Baker Professor of Chemistry The Johns Hopkins University and Richard J. Kokes Assistant Professor of Chemistry The Johns Hopkins University John Wiley & Sons, Inc., New York wfry the < ao. -ili- Crystal structure and oxides 0 o \vi be .res. ree. v of the :lle. his o Oxygen Silicon Fig. 15. The amphibole chain amphibole chain are of two types: one is bonded to two active oxvgens. and the other is bonded to one active oxvgen. The repeat unit, indicated bv the dotted ines. has the formula (SUO^6). Most of the commercial asbestos is an amphi bole and made up of such chains. To break a long chain, it is necessarv to break a chemical bond; hence individual chains are difficult to break. On the other hand, adjacent chains are held together bv weak forces and it is easv to separate them. These characteristics give rise to the fibrous nature of the solid. Sharing of three corners of the tetrahedra leads to the sheets pictured in Fig. 16. The active oxvgen above each silicon atom is not shown, and the drawing ^presents onlv part of an infinite sheet. The general formula tor this anion is LAM021525 Chemistry of Group I, II, and III elements 531 Bervllium can be prepared bv the electrolysis of a fused mixture of beryllium chloride. BeCl2. and sodium chloride. In metallic form, bervllium is used for making windows for X-rav tubes, since elements with low atomic number have \erv slight absorption for X-ravs. Beryllium is also useful in the production of alloys with special properties for springs. BeO is extremely poisonous, and this limits somewhat the uses of Be in industry. Magnesium (Mg) is found in nature as the carbonate, magnesite, and most abundantly in the form of silicates, including talc, soapstone, asbestos, and mica. Next to sodium, magnesium is the most abundant metal in sea water. Magnesium metal can be produced bv the electrolysis of fused magnesium chloride or bv the reduction of magnesium oxide bv carbon or bv an aliov of iron and silicon: MgO + C = Mg + CO 3MgO + FeSi ^3Mg + FeO + Si02 It is extensively used in light-weight ailovs for the construction of airplanes and rockets, but it has the disadvantage of oxidizing so readily that it must be regarded as an inflammable substance. In pure form, it burns verv rapidly even in air and is one of the principal constituents of flashlight powder. Calcium (Ca) is found widely in nature. Limestone consists of a mixture of calcium carbonate and siliceous compounds; calcite is a purer form of calcium carbonate. One of the most familiar forms of calcium carbonate is marble; it is also found in the shells of marine animals. Other sources of calcium are dolomite, MgC03 * CaCOa; gvpsum, CaSC>4 2H2O; anhvdrite, CaSO-i; fluorspar or fluorite, CaF2; phosphate rock, principally Ca3(PO.j)2. Bones of animals consist largely of calcium phosphate. There is considerable calcium present in sea water in the form of the doublv charged ions. Ca+2. Metallic calcium can be prepared bv the electrolysis of fused calcium chloride. CaCl2- It is used as a deoxidizer for iron and steel as well as copper: it is a constituent of some lead alloys. Strontium (Sr) is found-in a mineral called celestite (SrS04) and in strontianite 1 SrCOs). Barium (Ba) is found in a mineral barite (BaSCU). Because of its large atomic number, barium absorbs X-ravs strongly. When studies of the gastrointestinal tract are made, patients usually swallow a mixture of barium sulfate and water in order to make the organs stand out in the X-rav photograph or the fluoroscopic view. Although barium compounds are highly poisonous, the sulfate is so insoluble that the body does not absorb significant amounts. A green color is produced in fireworks bv barium nitrate. Ba(N03)2, and bv barium chlorate. Ba(C103)2- Compounds. The elements of this group have two electrons in the outer shell: B0C^376