Question

What does the atomic orbital diagram of carbon look like before `sp^3` hybridization?

Answer 1

Orbital hybridization is essentially a process of mixing orbitals together and spitting out new ones that are all identical in "symmetry" and "composition" to the orbital(s) from the other, incoming atom(s).

You can read more about `sp^3` hybridization here. The qualitative energies turn out to be the following:

with `sp^3` hybridized orbitals of `25%` `s` character and `75%` `p` character.

SIDENOTE: Because the `2p` orbital constitutes most of the `sp^3` orbitals (`75%`), and because the `2p` orbitals were higher in energy than the `2s` orbitals, the `sp^3` orbitals are closer in energy to the original `2p` orbitals than to the original `2s` orbital.