1.7.2 sp2 Hybrid Orbitals
When an s orbital combines with two p orbitals, three hybrid orbitals results that are oriented at 120° angles to each other. These orbitals are called sp2 hybrid orbitals. The remaining unhybridized p orbital perpendicular to the plane of the three sp2 hybrid orbitals. The 120° arrangement is called trigonal geometry.
For example, each carbon atom of ethene has three sp2 hybridized orbital and one unhybridized p orbital. The sp2 hybridized orbital of each carbon atom forms two σ -bonds by overlapping with s orbitals of two hydrogens and one σ -bond by overlapping with sp2 orbital of the other carbon atom. The sidewise overlap of the unhybridized p orbital of each carbon atom gives aπ-bond.
The positively charged carbon in the methyl cation is sp2 hybridized. It forms three covalent bonds using sp2 orbitals by overlapping with s orbital of hydrogen atom. Its unhybridized p orbital stands perpendicular to the plane and remains empty.
The carbon atom in the methyl radical is also sp2 hybridized. The methyl radical has one unpaired electron. That electron is in the unhybridized p orbital.
1.7.3 sp Hybrid Orbitals
When an s orbital and a p orbital of an atom combine, a sp hybridized orbital is formed. For example, each carbon atom of ethyne has one sp hybridized orbital and two unhybridized p orbitals. The two unhybridized p orbitals are perpendicular to each other. One end of the sp hybridized orbital overlap with s orbital of hydrogen and the other end overlap with sp hybridized orbital of the other carbon atom. Sidewise overlap of two unhybridized p orbitals gives aπ -bond. So ethyne molecule has one σ-bond and two π -bonds. These hybrid orbitals give a bond angle of 180° that leads to linear arrangement.
