Degenerate orbitals are those orbitals that have the same energy. In this article, we saw an overview of degenerate orbitals along with some examples. Thus, 2p-orbital has lower energy than 3s-orbital.Īlso read about Tips for UPSC Preparation Conclusion: When two orbitals have the same (n+l) value, then the orbital having a lower ‘n’ value has lower energy.Thus, 4s-orbital has lower energy than 3d-orbital, hence would be filled first. The orbital with the lower (n+l) value has lower energy.Here, n=principal quantum number and l=azimuthal quantum number (determines the orbital angular momentum). The energy of an orbital is determined by the (n+l) rule. Visit to know more about UPSC Exam Pattern Bohr-Bury’s Rule: The sequence of the energy of the orbitals is according to Bohr-Bury’s rule.For example, a shell with n=1 has only one subshell, 1s, and a shell with n=2 has two subshells, 2s and 2p. The number of subshells in a shell is equal to the principal quantum number ‘n’ of the shell.In order to remember the above sequence, a few things need to be kept in mind: For multi-electron atoms, the following sequence represents the increasing order of the energy of the orbitals.ġs, 2s, 2p, 3s, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s The Aufbau principle states that “electrons are added one by one into the various orbitals in order of their increasing energy starting with the lowest energy orbital”.Īccording to the Aufbau principle, electrons first occupy the lowest energy orbital available to them, followed by the filling of higher energy orbitals only when the lowest energy orbital gets completely filled up. “Aufbau” is a German term that means to construct or build up. The increasing order of the energy of different orbitals with different main energy levels was given by the Aufbau principle. The reason for it is that the only electrical interaction present is the attraction between the single electron and the nucleus.Ĭheck out the complete UPSC Syllabus Aufbau Principle However, it is only for a single-electron system, which only the hydrogen atom has. The energy of an electron increases with an increase in the principal quantum number.

A hydrogen atom contains only one electron, so the energy of that electron is only dependent on the value of the principal quantum number ‘n’ (which determines the energy of the shell).

4s 4p 4d 4f