Carbon has in all, six electrons, which are distributed in first two shells, i.e., K-shell has two and L-shell accommodates four electrons viz.,
This distribution indicates the use of two half-filled orbitals and therefore makes carbon to act as divalent. But, experimental observations indicate carbon to show tetravalency in the combined state. To account for tetravalency of carbon, it has been suggested that one of the 2s electrons unpairs and gets promoted to the vacant 2p
z orbital. This leads to the electronic configuration given below for the excited state.
Thus, the excited state has four unpaired electrons occupying four different orbitals opening the possibility for the formation of four bonds. This accounts for the tetravalency of carbon. The energy required for promoting 2s electron to 2p
z orbital is compensated by the energy released during bond formation (as in CH
4).
No comments:
Post a Comment