The ground state electron configuration of carbon is #"1""s"^"2""2s"^"2"2"""p""^2#. An excited state electron configuration of carbon is #"1""s"^"2""2s"^1"2p"^3"#. This is the state of carbon when it undergoes chemical bonding to form four covalent bonds, as in methane, #"CH"_"4"#. However, the experimental evidence shows that all four bonds have the same energy, which can only be explained by the concept that the 2s and 2p orbitals hybridize to form four #"sp"^3# orbitals, each with one unpaired electron.