Limitations to covalent bonding with s and p orbitals
(Using CH4 as an example)C forms 4 single covalent bonds with 4 Hs4 unpaired e-s from one C interacting with another 4 unpaired e-s from four HsGround state of C atom only have 2 unpaired e-s To give 4 unpaired e-s, electron can be excited from 2s orbital to the vacant 2p orbital
3 x C-H bonds originate from 2p orbitals (C) and 1s orbitals (H)
1 x C-H bond originates from 2s orbital (C) and 1s orbitals (H)
Latter seems shorter than the former but C-H bonds within CH4 are all of equal length.