Why hybridization occurs?

Answer 1

Hybridisation is a method used in valence bond theory to create atomic orbitals of the correct symmetry for bonding. this is just a "model" of a chemical bond which happens to give very good predictions of molecular geometry. Hybridising s and p orbitas can produc sp hybrids, linear, sp2 hybrids, trigonal planar and sp3 hybrids, tetrahedral.

An alternative approcah to bonding is molecular orbital theory which models the bonds without necessarily hybridising the atomic orbitals first. This gives a more complex view of bonding that explains energy levels in the molecule but doesn't readily predit geometry. At the bottom both theories or models of cchemical bonds work out to be the same.

Zosimus

I disn't write whats below but it gives the rationalisation of valence bond theory but igmores MO theory which does work with the unhybridised orbitals.

You know the electrons are only present to counter balance the positive nucleus.If you consider an electron nearer to nucleus(1s electron) it is of low energy but as it goes far away(2s electron) its energy is higher because of higher potential energy. If you consider 1s orbital the shape is spherical just because if you try to locate an electron for a span of about 1 second it would be found anywhere around the nucleus in form of a sphere, thats why s orbitals are spherical same for 2s orbitals but since energy increases in 2p orbitals they are in dumb bell shaped lobes but when you loook at the lobe you may wonder how electron would have traveled from one lobe to another without passing the intermediate space thats associated with wave nature of electrons.When tow hydrogen atoms combine they can combine without any trouble because they have same energy orbitals.But when an carbon atom which has outer orbitals having 2 electrons in 2s orbital and 1 electron in 2px and 1 electron in 2py orbital cannot combine with hydrogen 1s orbitals because of unequal energies in 2s and 2p orbitals. In order to overcome this 2s and 2p orbitals combine and distribute their electrons in space such that all have equal energies. for example in methane after carbon undergoes sp3 hybridization that means a s orbital had combined with 3 p orbitals , and there are 4 lobes in sp3 hybrid each has an electron and they can now bond with hydrogen easily than an unhybridized atom