How to determine the hybridization of an atom in a molecule?

To determine the hybridization of an atom in a molecule, you can count the number of regions of electron density around the atom. These regions can be bonds or lone pairs. Then, use the following guidelines:

• If there are 2 regions, the atom is sp hybridized.
• If there are 3 regions, the atom is sp2 hybridized.
• If there are 4 regions, the atom is sp3 hybridized.
• If there are 5 regions, the atom is sp3d hybridized.
• If there are 6 regions, the atom is sp3d2 hybridized.