Bonding models for the subvalent element chlorides

In the ground state electron configuration of the Group 14 atoms the two p electrons in the valence shell occupy different orbitals and have parallel spins. This atomic state has been labeled P. As a first approximation we assume that the two valence shell s electrons remain unaffected by formation of the two E-Cl bonds. Combination of each of the two 

We now turn our attention to a comparison of subvalent and Lewis-valent chlorides. Comparison of bond distances and MBEs shows that the bonds in the tetrachlorides, ECI4, E = Si, Ge, Sn or Pb are shorter, but weaker than the bonds in the dichlorides. We have already noted a similar difference between the Lewis-valent and the subvalent chlorides of the Group 13 elements. 

The C-Cl bond CCI4 is unusual in being longer than in in CCI2. Since there are six Cl Cl contacts in CCI4 as compared to just one in the dichloride, the C-Cl bonds in the tetrachloride may be elongated by Cl Cl repulsions. We shall return to this question at 

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