Degenerate Orbitals

Degenerate orbitals definition:

Electron orbitals which have the same energy levels are known as degenerate orbitals. As per Aufbau’s principle, the lower energy levels are filled before higher energy levels. As per Hund’s rule, the degenerate orbitals are filled evenly before they move to higher energy levels. Aufbau’s principle, Paulis exclusion principle, and Hund’s rule are three rules of electronic configuration.

What is Aufbau’s principle?

It states that in the ground state of an ion or an atom, the atomic orbitals of the electrons fill the lowest available energy levels before they occupy the higher levels. For instance, 2s subshell is filled after the 1s shell is occupied. Hence the most stable electron configuration is achieved.

What is Hund’s rule?

Hund’s rule states that the greatest number of parallel electron spins happen in the ground state electron configuration in any electron subshell. This rule was formulated by Friedrich Hund in the year 1927.

It helps in determining the ground state of a molecule or an atom.

They are reliable to determine the lowest state of an excited electronic configuration which is already given. For example, consider a helium atom. Hund’s rule correctly foretells that the 1s2s singlet state is higher than the 1s2s triplet state.

Degenerate orbitals example:

p orbital has 3 degenerate orbitals. All three have the same energy levels. Each orbital is first assigned with only one electron. The second electron will be of opposite spin. Each orbital is filled and the total is six electrons.

Explanation of Degenerate orbitals with the diagram

Orbitals in the 2p sublevel are degenerate orbitals – Which means that the 2px, 2py, and 2pz orbitals have the exact same energy. The below diagram will help you understand it better.

Similarly, at higher energy than 2p, the 3px, 3py, and 3pz are degenerate orbitals.

And at the 3d energy level, the 3dxy, 3dxz, 3dyz, 3dx2 – y2, and 3dz2 are degenerate orbitals with the same energy.

Degenerate orbitals diagram

A diagram representing the degenerate orbitals

Degeneracy – The total number of different states of the same energy is called degeneracy. It is also known as the degree of degeneracy.

  • The degree degeneracy of p orbitals is 3
  • The degree degeneracy of d orbitals is 5
  • The degree degeneracy of f orbitals is 7

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