In methane ($CH _{ 4}$) molecule all four carbon - hydrogen bonds are identical and bond angle HCH is 109°28'. How can we explain this?

[prasanna]

In excited state, carbon atom has three unpaired electrons in p-orbitals and one electron in s-orbital.These four valence electrons are with different energies. These orbitals combine to form four identical orbitals. Four hydrogen atoms form four identical C - H bonds with bond angle 109°28’. This is called hybridisation.