Professor Linus Pauling from California Institute of Technolgy in California suggested an interesting theory to explain the discrepancy. The theory also offers an explaination why carbon containing molecules can have one of three geometries around each carbon atom in the molecule. This hybridization theory resulted in Pauling being awarded the Nobel Prize for Chemistry. According to this theory, carbon atoms are capable of hybridizing the s and p valence orbitals in one of three different ways. This hybridization process is preceded by the formation of an excited state carbon atom where a 2s electron is promoted into a 2p orbital before the hybridization process begins.
Hybridization is similar to the hybridizations that occur in the plant and animal kingdoms.
This results in a hybrid species which has some of the characteristics of both parents. The 2s and 2p orbitals of the excited state carbon can form one of three types of hybridized atomic orbitals. Each of the four sp 3 orbitals has an unpaired electron explaining the tetra-valency for such an sp 3 carbon. The four sp 3 hybrid orbitals are arranged around the nucleus of the sp 3 hybridized carbon atom with the orbitals pointing toward the corners of a tetrahedron. The angle separation between the hybrid orbitals is 109 degrees.