Hybridization a scheme for linear species

The notation sp means that one s atomic orbital and one p atomic orbital mix to form a set of two hybrid orbitals with different directional properties. 

Equations 4.1 and 4.2 represent two wavefunctions which are equivalent in every respect except for their directionalities with respect to the x axis. Although the orbital energies of the initial 2s and 2p atomic orbitals were different, mixing leads to two hybrid orbitals of equal energy. 

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