Structure and bonding in simple compounds of the Group 17 elements

Structure and bonding in simple compounds of the Group 14 elements 

The first two elements in Group 14, carbon and silicon, have the electron configurations Ng]m np while the heavier elements, germanium, tin, and lead, have the electron configurations [Ng]( — l)d ns np. The properties of Sn and Pb are such that they are classified as metals, while Si and Ge are classified as non-metals or metalloids. Carbon is definitely a non-metal. We shall use the symbol E (for Element) to denote any member of the group. 

The oxidation numbers of the C atoms in CH4 and CCI4 are -4 and 4-4 respectively. The oxidation number of the central carbon atom in C(CH3)4 is zero. Minimum energy rupture of a bond in CH4 or CCI4 or a C-C bond in C(CH3)4 yields neutral, radical species. These bonds are therefore classified as homolytic bonds. We shall refer to the number of (single) homolytic bonds that an atom forms, as the valency of the atom. The central atoms in the compounds EH4, E(CH3)4 and ECI4 are all tetravalent. 

All the tetrachlorides form liquids at room temperature. The C, Si, Ge and Sn tetrachlorides are stable, but the lead analogue decomposes explosively at temperatures above 20 C to yield chlorine and a solid dichloride  

Solid dichlorides of tin and germanium are also known. Evaporation yields monomeric Pb, Sn, or Ge dichlorides in the gas phase. Monomeric CCI2 or SiCh may be generated and studied in high temperature vapors. We shall refer to Group 14 atoms that form four homolytic bonds as Lewis-valent and to atoms that form two homolytic bonds as subvalent. 

---