Carbon forms covalent bonds with other carbon atoms and also with other elements like hydrogen, oxygen, halogens, nitrogen, sulphur etc. The formation of these covalent bonds and the tetravalence of carbon is because of its electronic configuration and the hybridization of s and p orbitals. The simplest compound of the alkane series is methane in which carbon is sp3 hybridised and forms bonds with four hydrogen atoms to form a tetrahedron where carbon is in the centre and the hydrogens at the four corners. Similarly the shapes of other molecules like ethane (C2H6),ethene (C2H4) and ethyne (C2H2) can be explained by using sp3 , sp2 and sp hybridization.
As we more from sp3 to sp2 to sp hybridization, the s character increases from 25% to 33% to 50% respectively. Greater the s character, closer the electrons are to the nucleus, more effective the overlap with other orbitals and thus shorter and stronger bonds are formed. Thus bond length decreases and bond strength increases with increase in s character. In other words, electronegativity increases as s character increases. Thus a carbon having sp hybridization is more electronegative than a carbon in sp2 hybridization which is more electronegative than a carbon having sp3 hybridization.
