Hybridized centers:

All the atoms in an organic structure (apart from hydrogen) are sp, sp² or sp³ hybridized.

Figure: Examples of sp, sp² and sp³ hybridized centers.

The recognition of sp, sp² and sp³ centers is very simple if you keep in mind the following rules:

• All atoms connected by a single bond are sp³ hybridized (apart from the hydrogen).
• Both carbon atoms included in the double bond of an alkene (C=C) have to be sp² hybridized.*
• Both the carbon and the oxygen of a carbonyl group (C =O) have to be sp² hybridized.
• All aromatic carbons have to be sp² hybridized.
• Both atoms included in a triple bond have to be sp hybridized.
• Hydrogen employs a 1s orbital for bonding and is not hybridized.

Hydrogen atoms cannot be hybridized. They can just only bond through using an s orbital because there are no p orbitals in the first electron shell. Hence it is not possible for hydrogen to be included in π bonding. Alternatively oxygen, nitrogen and halogens can form hybridized orbitals that are either included in bonding or in holding lone pairs of electrons.