Carbon and silicon are mainly tetravalent while germanium, tin and lead also show divalency. Explain.

Explanation

This is explained on the basis of inert pair effect which is significant only in elements with large values of atomic numbers. The general electronic configuration of the elements is `ns^(2)np^(2)`. Because of inert pair effect, in case of `1^st` three elements, the valence `p-`electrons readily become available for bonding while the valence x-electrons remain attached to the nucleus. Thus, these elements show divalency while the first two elements in the absence of inert pair effect are tetravalent.