Degenerate: definition in chemistry
Degenerate: Describes orbitals or other quantum states that have exactly the same energy, such as the three p orbitals of one sublevel.
In an isolated atom, all the orbitals of one sublevel are degenerate, so the three 2p orbitals share one energy and the five 3d orbitals share another. Hund's rule describes how electrons fill degenerate orbitals: one at a time first, then in pairs. Degeneracy can be broken, or split, by an atom's surroundings: in a transition metal complex, the attached molecules or ions give the d orbitals slightly different energies, which is why many such compounds are colored.
Examples
- The three 2p orbitals of a free carbon atom
- The five 3d orbitals of an isolated iron atom
- In a hydrogen atom, the 2s and 2p orbitals have the same energy
- In [Ti(H₂O)₆]³⁺, split 3d orbitals give the ion a purple color
On the periodic table
The widths of the s, p, d and f blocks, 2, 6, 10 and 14 columns, match the number of electrons that 1, 3, 5 or 7 degenerate orbitals can hold.