Why is it believed that a carbon atom must form hybrid electron orbitals when it bonds to hydrogen atoms to fo

Question

Why is it believed that a carbon atom must form hybrid electron orbitals when it bonds to hydrogen atoms to form methane?

Answer 1

It is because of the bonding orbitals of hydrogen and carbon. The electron configuration of carbon is 1s2 2s2 2px1 2py1 which would indicate that carbon is only capable of having 2 bonds, 2px and 2py, (failure of valence bond theory) when in fact one of the electrons in the 2s2 orbital is promoted to the 2pz orbital giving 1s2 2s1 2px1 2py1 2pz1. This promotion requires energy which is more than recovered by the greater strength and number of bonds formed. This process is not a 'real process' but a contribution to the overall process of bonding.

Then there are 4 bonds from carbon to hydrogens in a tetrahedral shape. Each of these sp3 hybridized bonds is a sigma bond between the carbon orbital and the hydrogen orbital at one corner of the tetrahedron resulting in 4 equivalent hybrid bonds.

I learned this in PChem but here are some sites that explain what I have said:
http://www.chem.uncc.edu/faculty/murphy/1251/slides/C19b/sld006.htm
http://web.uccs.edu/cjohnson/chem103/pp/Lec30.ppt

I hope that this helps.

Answer 2

It is believed to be so because Carbon bonds with H are strongly directional in nature unlike pure atomic orbitals and differ significantly in energy.