Hybridization occurs when atomic orbitals blend to form new atomic orbitals. Covalent bonds form when the atomic orbitals of two atoms overlap.
According to VSEPR theory, `BeCl_2` has a linear molecular geometry. This molecular geometry cannot be obtained by using `s, p` and `d` orbitals. Hybridization of the `2s` with one of the unoccupied `2p` orbitals in Be is the solution. The two `sp` hybrids of `Be` overlap with 3p orbitals of two ` Cl` atoms and form two bonds with bond angle of` 180^o`.
Beryllium needs two hybrid orbitals for the two sigma bonds. The two unhybridized `2p` orbitals of ` Be` remain unoccupied.
The number of the atomic orbitals mixed equals the number of hybrid orbitals. The types of atomic orbitals fused influence the types of hybrid orbitals.