What is so special about carbon that they devoted a whole branch of chemistry to it?

Answer 1

Carbon has some very important properties. It forms four bonds, and that is the highest number of bonds that any element forms, which gives it the capability of forming more complicated types of molecules than most other elements. There are, of course, other elements in group 4, that also form four bonds, such as silicon. However, carbon is the lightest element in that group, as as you go down the Periodic Table to heavier elements in that group, you get lower electronegativity, or in other words more metallic type of bonding, as compared to the non-metallic type of bonding that carbon forms, and this is significant because carbon can form moderately strong bonds with various elements such as hydrogen, oxygen, and nitrogen (etc.) but the more metallic elements of group 4 form stronger and more permanent bonds (compare the properties of carbon dioxide and silicon dioxide - quite a difference!). So as it turns out, only carbon gives us the versatility that is needed to form the basis of biochemistry. There can be no life without carbon. It is not for nothing that Star Trek refers to humans as a carbon based life form.