Degenerate Orbitals: Detailed Explanation, Example and Sample Questions

Degenerate Orbitals are the orbitals having the same levels of energy. These orbitals are associated with various principles like Aufbau Principle, Hund’s rule, and Pauli’s Principle which helps us understand the basic manner in which the electrons are distributed in the orbitals. 

Key Takeaways: Degenerate orbitals, electronic structure, covalent bonding, Hund’s rule of multiplicity, Aufbau Principle, electrons.

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What are Degenerate Orbitals?

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The electrons orbitals of equal energy levels are known as Degenerate Orbitals. The electrons of the orbitals are not affected by any external factors, like an electric or magnetic field. The application of the magnetic field is disrupted by the degeneracy of these orbitals.

Degenerate Energy Levels 

Read More: Shapes of Atomic Orbitals

Example of Degenerate orbitals

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An atom has four orbitals which are s, p, d, f. All the p orbitals, p_x, p_y, p_z, are having the same energy as the p-orbital. Hence, they can be called degenerate orbitals. Every orbital, at first, consists of one electron, the second electron has to be of the opposite spin. In the end, there are 6 electrons possessed by three orbitals. Therefore, the p-orbital is filled.

Read More: Cannizzaro Reaction Mechanism

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Hund’s Rule of Multiplicity

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According to Hund’s rule of Multiplicity, stated by Friedrich Hund:

• Electrons are responsible for filling the Degenerate Orbitals.
• In a sub-shell, one electron is added to each of the degenerate orbitals before two electrons are added to any orbital.
• Electrons are added always to a subshell having the same value of the quantum spin number till each orbital in that subshell possesses at least one electron.
• Hund’s rule of multiplicity states that, in a given electronic configuration, electron pairing in p, d, and f orbitals cannot take place until each electron in a sub-shell possesses one electron each. Suppose, the electronic configuration of an atom of Carbon is 1s²2s²2p². So, the orbital will be occupied by two 2s electrons and the different orbitals will be filled with two electrons (2p) as per Hund’s rule. 

The diagram below explains the correct order by which the orbitals are filled with electrons:

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 Aufbau Principle

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Electrons in an orbital are filled in the order from lower to higher energy levels. The lower energy level of the orbital gets filled first as stated in Afbau’s Principle. This principle is highly responsible for stating the type of chemical bond which an atom can form. Aufbau’s Principle is utilized to determine the electronic configuration of an ion or an atom.

Aufbau Principle - Filling of orbitals

Read More: Franck Hertz Experiment

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Detailed Explanation for Degenerate Orbitals

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There are three orbitals present in the 2p sub-shell as 2P_x, 2P_y, 2P_z orbitals. In a similar way, electrons fill in the degenerate 3p orbital that is 3p_x, 3p_y, 3p_z. All the orbitals are having similar energy levels. Electrons in the 4P orbitals are also having similar energy and are filled as 4px, 4py, 4pz. Hence 2P, 3P & 4P are all degenerate molecular orbitals. In the case of the d orbital, it consists of 5 degenerate orbitals which are 3d_xy, 3d_yz, 3d_xz, 3d_x^2-_y², 3d_z². Hence, the degrees of the degeneracy of the orbitals are similar to the energy.

Degeneracy: The total number of the different states having the same energy is known as degeneracy. The value or degree of degeneracy is:

• For p-orbital: 3
• For d-orbital: 5
• For f-orbital: 7

It is noticed that fully filled and half-filled orbitals degenerate orbitals have extra stability because of their symmetry.

Read More: Charge to Mass Ratio of Electron

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Things to Remember

• Degenerate Orbitals are the ones with the same levels of energy.
• The elements whose all the orbitals are filled are the most stable atoms and they do not react with other elements.
• In the ground-state electron configuration, the greatest number of the parallel electron spins happen to spin in any subshell as stated by Friedrich Hund.
• According to Aufbau Principle, the electrons will be filled from lower energy levels to higher energy levels.
• The degeneracy values of orbital p, d, and f are 3, 5, and 7 respectively.
• There are three degenerate orbitals present in P orbital - P_x, P_y, P_z and five degenerate orbitals present in d orbital - d_xy, d_yz, d_xz, d_x^2-_y², d_z².
• Degenerate Orbitals is a sub-topic of the chapter Structure of Atom. This particular section carries 2-3 marks and the overall chapter carries 10-11 marks in CBSE Class 11 Examination.