Hybridization of Atomic Orbitals I

s and p orbitals overlapping to form covalent bonds cannot yield the various molecular shapes in the VSEPR model. Valence bond theory helps to explain this molecular geometry through the hybridization, or mixing, of atomic orbitals. 

Some atomic orbitals involved in bonding recombine to form new orbitals whose shapes are a hybrid of the originals. The initial number of atomic orbitals and the number of hybrid orbitals generated is always the same. 

Beryllium fluoride is a linear molecule. The beryllium atom has two valence electrons found in its 2s orbital in the ground state.  

The s orbital mixes with one of the empty p orbitals to create orbitals that contain unpaired electrons available for bonding. This leaves two unhybridized p orbitals and produces two sp hybrid orbitals, named for the original atomic orbitals.

The hybrid orbitals have a different shape from their constituent atomic orbitals with one lobe that is significantly larger than the other. Thus, the electron probability density is highly concentrated in a directional lobe, which leads to a more effective overlap with the orbitals of other atoms. For clarity, these orbitals are often shown without the minor lobes.