Group IVA elements

Covalent radius (A) Ionic radius (A)(xx) Ionization enthalpy (cV) Crystal Structure 

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Titanium monosulfide, TiS, assumes two forms, both of which are of the NiAs type. In 384, the packing of sulfur is of the ABAC type, with alternate layers of metal sites being fully occupied but the intermediate sites half filled. A series of intermediate phases Ti2+xS4 (0.2 < x < 1) also occurs. The trisulfide TiS3 is best represented as TiS (S2) . The trichalcogenides of Group IVA elements are typified... 

Alkyls of group IVA elements are essentially unreactive in air, but group IIIA alkyls are extremely reactive. Provide an explanation for this great difference in behavior. 

The +4 oxides of the group IVA elements are generally acidic (as is C02) or amphoteric in character. As shown here for C02/ acidic oxides form oxyanions,... 

One of the most common types of reactions carried out to prepare organic derivatives of the group IVA elements is that of transferring an alkyl group by means of a Grignard reagent. Alkylation of SnCl4 can be illustrated as follows ... 

By employing sequences of reactions of these types, the organic chemistry of the group IVA elements has become a vast area at the interface of inorganic and organic chemistry. 

In addition to the types of compounds discussed so far, the group IVA elements also form several other interesting compounds. Silicon has enough nonmetallic character that it reacts with many metals to form binary silicides. Some of these compounds can be considered as alloys of silicon and the metal that result in formulas such as Mo3Si and TiSi2. The presence of Si22 ions is indicated by a Si-Si distance that is virtually identical to that found in the element, which has the diamond structure. Calcium carbide contains the C22-, so it is an acetylide that is analogous to the silicon compounds. 

Substituents are named as one of several classes. The most important ones are dealt with here. For monoatomic radicals from borane, methane, silane (and other Group IVA elements) they are named by replacing the ane ending by yl, i.e., ylene and ylidyne, to denote the loss of one, two, or three hydrogen atoms, respectively ... 

The stereochemical correspondence between trimesitylmethane and trimesitylsilane extends to other Group IVA elements. Thus the barrier to enantiomerization by a two-ring flip mechanism for trimesitylgermane is AG 80 9.2 kcal/mol. 47>... 

The bivalent substitutional impurities of group-IVA elements such as C, Si, Ge, Sn, or Pb also produced double shallow acceptor levels with the ionization energy of 0.721 eV for C, 0.919 eV for Si, 0.792 eV for Ge, 1.034 eV for Sn, and 1.283 eV for Pb, respectively. Some bivalent substitutional impurities of another type of group-VIIIA elements such as Ne, Ar, Kr, or Xe did not produce any energy levels in the band gap by the substituting host O atom. As expected, the acceptor levels produced by the impurities of group-VA and -IVA elements at the O site were single or double acceptors, respectively. Quantitave analysis of these shallow acceptors produced by the monovalent and bivalent substitutional impurities will be made in Section 4.2. 

There is a much more extensive chemistry of the +4 oxides of the Group IVA elements than there is for the +2 oxides. In general, the E02 compounds are acidic or amphoteric oxides, and they show this characteristic by forming oxyanions. This type of behavior has also been illustrated for C02 by the reaction... 

Although the oxides of all the Group IVA elements are of some interest, the chemistry of Si02 is by far the most complex. Unlike C02 where double bonding results in the molecule having the structure... 

The tetrahalides of the Group IVA elements hydrolyze to give the oxides, hydroxides, or hydrous oxides (E02, E(OH)4, or E02 2H20). Typical processes of this type are represented by the equations... 

By utilizing combinations of these types of reactions, an extensive organic chemistry of all of the Group IVA elements can be developed. 

Sulfide compounds are formed by all of the Group IVA elements, and lead is found as the sulfide in its principle ore galena that has Pb2+ and S2 ions in a sodium chloride lattice (see Chapter 3). A chain structure is shown by SiS2 in which each Si is surrounded by four S atoms in an approximately tetrahedral environment ... 

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