The Group IVA Elements

Although silicon compounds have been used since the earliest times, the element was not obtainable until advances in technology came about. Minerals containing silicon include sand and silicates that are widely distributed (silicon constitutes approximately 23% of the earth s crust), and they have been used in making glass, pottery, and mortar for many centuries. In addition to these uses, silicon is now highly purified for use in integrated circuits (chips) and as an alloy known as Duriron that has many uses. Silicon has the diamond structure with a density of 2.3 g/cm3. 

Although germanium was unknown, Mendeleev predicted the properties of the missing element (which he referred to as ekasilicon) based on the properties of other elements. While analyzing the mineral argyrodite, Winkler found that it contained about 7% of some element that had not been identified, 463 

Reduction of the oxide is then accomplished with hydrogen. 

Germanium is one of the materials that is used in producing semiconductors. When combined with phosphorus, arsenic, or antimony (which have five valence electrons), an n-type semiconductor results, and when combined with gallium (which has three valence electrons), the product is known as a p-type semiconductor. 

Many of uses of tin are also those of lead, because the metals form useful alloys. When lead is alloyed with a few percent of tin, it becomes harder and more durable. Although other compositions are produced, common solder consists of about an equal mixture of tin and lead. An alloy known as type metal contains about 82% Pb, 15% Sb, and 3% Sn, and pewter contains approximately 90% tin that is alloyed with copper and antimony. Babbitt, an alloy used in making bearings, contains 90% Sn, 7% Sb, and 3% Cu. Tin is also used to coat other metal objects to retard corrosion, and a tin-niobium alloy is used in superconducting magnets. 

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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. 

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 ... 

I The e tron-acceptor ability of the Group IVA elements increases with a rise in their atomic number and, consequently, in the atomic radius. From the standpoint of structural chemistry this is, for instance, clearly illustrated by the structure of (CH3)3MCN crystals (M = Si, Ge, or Sn) in which a minimum intermolecular non-covalent contact betw n M and N atoms is 366 357 and 249 pm respectively. When M = Si this distance corresponds to the... 

Fig. 7. Comparison of the eigenvalues of the ns, npij and np /z electrons in the group-IVA elements using DFS calculations. This figure illustrates the very strong dependence of the spin-orbit splitting between the two p states as a function of the atomic number. For element 164, the 9s and levels are also drawn (85)...

Write names and symbols for (a) the alkaline earth metals, (b) the Group IVA elements, (c) the Group VIB elements. 

Separations of hydrides of silicon and germanium have been achieved by GC on ester and silicone phases. Separation of alkyltin mono- and dihydrides by GC requires the use of most inert stationary phases to preclude on-column reaction. Among the Group IVA elements, lead alone has hydrides for which GC has not proved possible. 

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