phosphorusand sulphur ever shows multiple valency why some elements shows multiple valency
Answers
Phosphorous and Sulphur both have electrons that have entered the 3rd shell s, p, d orbitals. In phosphorus, the configuration is 3s^2 3p^3 3d^0. The d orbital is empty and 1st and 2nd shell is completely filled. Now, when forming a bond, the atom often gets to an excited state due to which, the two paired electrons in the 3s orbital get separated and one electrons gets excited into the D orbital. So, now the configuration becomes 3s^1 3p^3 and 3d^1. If we follow hunds rule, we will know that all five electrons are now the configuration becomes 3s^1 3p^3 and 3d^1. If we follow hunds rule, we will know that all five electrons are now unpaired and thus can formed five bonds now as opposed to only three in unexcited state. It is similar in Sulphur. Thus, elements from third period onwards have multiple valency as they can form one number of bonds in non excited state and another number of bonds in excited state due to presence of d orbital.