Question

Why can't sulphur form as many bonds ,allotrpes as carbon , although both of them have the same valency of 4?,

Answer 1

Unlike carbon, sulphur chains do not meet the criteria of forming life. Carbon build the skeleton of life not only because it can form long chains, but more importantly, because of the diversity of its compounds. A carbon has 4 valence electrons and can form 4 bonds. Therefore, a carbon chain can have side chains, or bond with other elements (especially functional groups), or form double or triple bonds without having to break the chain. In Sulphur chains, however, each atom only has 2 bonds and after forming the chain they can virtually do nothing. We can of course persuade S to form more than 2 bonds, like in H2SO4, but then their electronegativities change too much with the additional atoms, and it’s not possible to form long chains anymore. For carbon, the electronegativity almost remain the same when it binds to H.