Hybridization is a process in which atomic orbitals are mixed to form new hybrid orbitals, usually of lower energy (more stable). Sp3 hybridization occurs when one s and three p orbitals (px, py, and Pz) are mixed to give a total of four sp3 orbitals. This type of hybridization occurs when an atom is surrounded by four groups of electrons.
Let’s consider the bonding in methane: CH4. Each carbon atom has four valence electrons. The electronic configuration of carbon looks like this in the ground state:
The first step in hybridization is the promotion of one electron from the filled 2s orbital to the empty 2pz orbital. Now all the 2s and 2p orbitals are singly occupied like so in their excited states:
The second step is the rearrangement of these orbitals into 4 degenerate sp3 hybrid orbitals.
Thus, the 2s and 2p orbitals each have one electron present. The total energy of these four orbitals is lower than the energy of the orbitals in the ground and excited state, the hybridized sp3 state of carbon in methane (and most organic compounds) is preferred. Carbon is in a more stable and lower-energy state when hybridized.