What are sp2 hybrid orbitals?
Aluminum number 13 has three valance electrons. One of the two electrons in the s orbital can promoted to a p orbital. There is one electron originally in the one of the three p orbitals. With the new promoted electron this gives 2 p orbitals each with 1 electron and 1 s orbital with 1 electron. These three orbital hybridize to form three
Now Aluminum has three equal orbitals that can be used for a bonding giving Aluminum a charge of +3 and a triangular planar configuration.