Nonmetals Silicon

The group 4A elements exemplify the increase in metallic character down a group in the periodic table Carbon is a nonmetal silicon and germanium are semimetals and tin and lead are metals. The usual periodic trends in atomic size, ionization energy, and electronegativity are evident in the data of Table 19.4. 

The nonmetal silicon forms two oxides, SiO and Si02. The monoxide is relatively unimportant, while silicon dioxide is a compound of major value in many chemical processes and products. 

This section presents a brief overview of a few other compounds that have not been described in previous sections. Because it can function as a nonmetal, silicon forms sihcides with several metals. These materials are often considered as alloys in which the metal and silicon atoms surround each other in a pattern that may lead to unusual stoichiometry. Examples of this type are Mo3Si and TiSi2. In some sihcides, the Si-Si distance is about 235 pm, a distance that is quite close to the value of 234 pm found in the diamond-type structure of elemental silicon. This indicates that the structure contains Si22-, and CaSi2 is a compound of this type. This compound is analogous to calcium carbide, CaC2 (actually an acetylide that contains C22- ions (see Chapter 10)). 

Based on the trends discussed in Chapter 6, the metallic properties of the elements in group 4A should increase as the atomic number increases. Carbon is a nonmetal silicon and germanium are metalloids tin and lead are metals. With such a wide range of properties, there are few rules that apply to all members of the group. One general trend does apply. The period-2 element, carbon, is not representative of the other elements within the group. 

The next two series of nonmetals, silicon through chlorine and germanium through krypton, show a maximum coordination number of. six in hexafluoro anions., SF . and TcF. Even here the oxyacids and oxyanions typically. show a coordination... 

Metalloids have some chemical and physical properties of metals and other properties of nonmetals. In the periodic table, the metalloids lie along the border between metals and nonmetals. Silicon (Si) is probably the most well-known metalloid. Some metalloids such as silicon, germanium (Ge), and arsenic (As) are semiconductors. A semiconductor is an element that does not conduct electricity as well as a metal, but does conduct slightly better than a nonmetal. The ability of a semiconductor to conduct an electrical current can be increased by adding a small amount of certain other elements. Silicon s semiconducting properties made the computer revolution possible. 

Metalloids The elements in the green boxes bordering the stairstep line in Figure 6.5 are called metalloids, or semimetals. Metalloids have physical and chemical properties of both metals and nonmetals. Silicon (Si) and germanium (Ge) are two important metalloids, used extensively in computer chips and solar cells. Silicon is also used to make prosthetics or in lifelike applications, as shown in Figure 6.6. 

Elements in the carbon group increase in metallic character going down the group. Carbon is a nonmetal. Silicon and germanium are metalloids. Tin and lead are metals. 

The group 14 elements all have electronic structures with four outer electrons (s p ) and no partly filled inner shells. The group shows the common trend toward metallic character with the heavier elements thus carbon is a typical nonmetal, silicon and germanium are metalloids, and tin and lead are characteristically metallic. As observed with other groups, the first member of the group is quite different from the rest. The carbon atom is smaller and has a higher ionization potential, both favouring predominance of covalence, but additional factors are ... 

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