Main-group elements. See

Figure 14. Homoleptic bis(dithiolene) units centered on main group elements (see text for references).

Several reviews have appeared describing metal-carbonyl complexes incorporating bismuth and the other heavy main group elements (see Cluster Compounds Inorganometallic... 

For a review of similarity and difference of chemical bonding between lighter and heavier main group elements, see W. Kutzelnigg, Angew. Chem., Int. Ed. Engl., 23, 272, (1984). 

For a recent review on multiple bonds between heavier main group elements see P. P. Power, Chem. Rev. 1999, 99, 3463-3503. 

E. H. Appelman, Astatine, Chap. 6 in MTP International Review of Science, Inorganic Chemistry, Series 1. Vol. 3, Main Group Elements Group VII and Noble Gases. pp. 181-98, Butterworths, London, 1972 see also ref. 23, pp. 1573-94, Astatine. 

Main-group elements, 153t Malleability The ability to be shaped, as by pounding with a hammer characteristic of metals, 244 Maltose, 618-619 Manometer, 104 Maple syrup, 277-278 Mass An extensive property reflecting the amount of matter in a sample, 7. See also Amount, critical, 525... 

The product of the second reaction is sodium aluminate, which contains the alumi-nate ion, Al(OH)4. Other main-group elements that form amphoteric oxides are shown in Fig. 10.7. The acidic, amphoteric, or basic character of the oxides of the d-block metals depends on their oxidation state (Fig. 10.8 also see Chapter 16). 

See for example A. G. Massey, Chemistry of Main Group Elements, Wiley, Chichester, 2000. 

The number of outermost electrons is crucial to the chemical bonding of the atom. (See Chap. 5.) For main group elements, the number of outermost electrons is equal to the classical group number, except that it is 2 for helium and 8 for the other group 0 (18) elements. (It is equal to the modern group number minus 10 except for helium and the first two groups.)... 

Two approaches have been used in the synthesis of these types of compounds. Small boron-phosphorus ring compounds can serve as building blocks, and addition and elimination reactions with other main group elements can then extend the cage structure (see Schemes 23 and 24, Section 12.12.6.4.5). Alternatively, an unsaturated carbenoid fragment can be added to the bicyclic fragment as illustrated in Scheme 31 <1998IC490>. 

While the generalizations of an earlier period were invaluable in the initial structuring of the chemistry of Main Group elements, we now see that they provided only a skeleton. The present picture of Group 14, as of the rest, is one of a rich chemistry of each individual element, a subtly varying relationship between them, and sufficient unexpected and at present unique behaviour to indicate that further development will be exciting and complex. 

Today the chemistry of diborane and the polyboranes is well understood [2] and much of it is textbook knowledge. Therefore, after a brief survey, emphasis will focus on the development of polyhedral borane chemistry within recent decades, and even restricting discussions to homopolyboranes only certain areas can be dealt with. This incorporates synthetic procedures, the chemistry of some polyboranes and particularly polyborane anions. Other chapters of this book are devoted to heteropolyboranes such as the carbaboranes (see Chapter 3.1), azaboranes and related heteropolyboranes (see Chapter 3.3) of the main group elements. In these areas enormous progress has been achieved within the last two decades. 

The octet rule is one of the cornerstones of chemical bonding theory. While the vast majority of molecules conform, apparent exceptions occur for molecules incorporating second-row (and heavier) main-group elements. Apparent refers to the fact that molecules such as dimethylsulfoxide and dimethylsulfone may either be represented in terms of structures with ten and twelve valence electrons, respectively, surrounding sulfur, or as zwitterions with the normal complement of eight valence electrons (see also discussions in Chapters 5 and 16). 

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