Pre-requisite Reading- Valency of Elements, Modern Electronic configuration, Atomic orbitals, Concept of Hybridization
sp3 hybridization of Carbon
Of the three states of hybridization - sp3, sp2, and sp, an sp3 (pronunciation: ess-pee-three) hybridization of Carbon is used to explain its tetravalency, shape, and equivalency of its four bonds.
Carbon (atomic number Z=6) in an unbonded state (ground state) has an electronic configuration of 1s2 2s2 2px1 2py1. The electrons in the 1s atomic orbital are called the core electrons. The core electrons are the ones closest to the nucleus, experiencing maximum attractive force and therefore do not participate in any bonding reactions. The electrons in the 2s and 2p atomic orbitals are called the valence electrons, and they take part in bond formation reactions.
The 2s and 2p atomic orbitals are separated by an energy gap with the 2s orbital being lower in energy than the 2p atomic orbitals. When Carbon gets a chance to form bonds with other atoms, mainly atoms of the p-block (Carbon, Hydrogen, Halogens, Oxygen, Nitrogen, etc., ) it excites one of the two electrons in the 2s atomic orbital of the ground state carbon atom to jump to the higher energy empty 2pz orbital.
The result is the mixing of the 2s and the 2p atomic orbitals to form a new set of four hybrid orbitals having newer identities. These four hybrid orbitals are equivalent in energy and do not have an energy gap like 2s and 2p of the parent atomic orbitals. Their energy lies in the middle of 2s and 2p but little closer to 2p than the 2s atomic orbitals. The shape of the hybrid orbital is similar to the p-orbital but having one lobe significantly larger than the other.
The four hybrid orbitals of Carbon now spread away from each other to avoid any interelectronic repulsions, and the angle at which it is minimum is 109.5o. The hybrid orbitals with one unpaired electron each now overlap with the single electron present in the atomic orbital of the incoming atoms and form single covalent bonds or the sigma bonds. The Carbon mainly forms such sigma bonds with the other elements of the p-block- Hydrogen, Oxygen, Halogens, Carbon, etc. only. The energy is released on the bond formation, and it compensates for the energy absorbed for the excitation of the electrons. The stimulus for the entire process is the formation of four new bonds for the Carbon, and the shape is tetrahedral.
As, one s and three p orbitals were involved in the excitation, hybridization and subsequent formation of bonds, such carbon is called as an sp3 hybridized carbon. (Read the definition of a sp3 hybridized carbon)
Examples of other atoms other than Carbon that is sp3 hybridized are- H2O, NH3, PCl3, interhalogen compounds (ClF, BrF, BrCl, ICl, IBr). These molecules have different shapes and bond angles (other than tetrahedral and 109.5o) to avoid inter-electronic repulsions of the lone pair and the bond pair.