Unhybridised

Unhybridised describes orbitals or atoms that have not undergone orbital hybridisation. In chemistry it refers to atomic or molecular orbitals that retain their original character—such as pure s or p orbitals—rather than mixing to form new hybrid orbitals used for sigma bonds.

In carbon chemistry, much bonding is explained by hybridised orbitals (such as sp3, sp2, or sp). However, some orbitals can remain unhybridised and participate in pi bonding or house lone pairs. For example, in ethene, each carbon uses sp2 hybrid orbitals to form sigma bonds, leaving one unhybridised p orbital on each carbon to form the C=C pi bond. In a benzene molecule, carbons are described as sp2 hybridised with unhybridised p orbitals that combine to create the delocalised pi system.

The term is most common within valence bond theory, where it helps distinguish sigma bonding formed by hybridised orbitals from pi interactions involving unhybridised p orbitals. In some teaching contexts, molecular orbital theory provides a broader description that does not rely on the concept of explicit hybrid orbitals, but unhybridised orbitals remain a useful shorthand for describing certain bonding patterns and reactivity.

Unhybridised orbitals can also appear in other elements and coordination environments, such as d- or f-orbitals in transition metals, where ligand fields and electron configurations influence whether orbitals participate in bonding in a hybridised or non-hybridised manner.