Homopolar bonding strength

The presence of a completed d shell markedly raises the ionization potential of the element. The explanation of this phenomenon is related to the theory of the homopolar bond the additional mutual interaction of the s and d electrons evidently increases the strength of the attraction energy between the s electron and the atom. 

A striking feature of the chemistry of carbon is the ease with which its atoms combine with one another. The strength of the C—C single bond is exceptionally high for a homopolar bond. But the Si—Si single bond is much weaker than that between silicon and either chlorine or oxygen, elements which are so much more electronegative than silicon. 

ELF. - In order to understand depleted homopolar bonds better Llusar et performed an ELF study of the N-N, 0-0 and F-F bonds. Deformation density maps are known to show a depletion of p between formally covalent bonds. However a topological analysis of the ELF function demonstrates that bond strength appears to be correlated with the disynaptic basin populations. From a qualitative point of view, the splitting of a disynaptic basin into two monosynaptic ones upon bond stretching is the signature of the covalent bond. 

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