Electronic Configuration of Elements and Stability of Orbitals (For CBSE, ICSE, IAS, NET, NRA 2022)

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Electronic Configuration of Elements

An atom of an element has different shells, sub-shells and orbitals and the distribution of electrons in these shells is called the electronic configuration. Electronic configuration of any orbital can also be represented by simple notation


  • number of main or principle shell or the principal quantum number
  • symbol of sub-shell or orbital
  • no. of electrons presents in that orbital

For example, means that the p sub-shell in the main shell contains 2 electrons.

  • In order to fetch full electronic configuration of an atom, these notations are written one after the other in the increasing order of the orbital՚s energy.
  • The filling of electrons in orbitals always starts from the orbital having the lowest energy with the electrons occupying the lower energy orbitals first.

Electronic configuration of few elements is given below:

  • Helium
  • Beryllium
  • Carbon
Electronic Configuration of Elements

Electronic Configuration of Elements

  • In order to make the electronic configuration of the elements simple and convenient, it is written such that the electronic configuration of noble gas core precedes the valence shell electrons. It represented by the symbol of noble gases using square brackets followed by the valence shell configuration.
  • For magnesium, the electronic configuration is written as and calcium are represented as There are a certain set of rules and principals that govern the filling of electrons in an orbital.

Configuration of Anions and Cations

  • Anions՚ electron configuration involves the addition of electrons following the Aufbau principle. First, we place an electron to occupy the outermost sub-shell and then proceed to fill the next higher orbital. For instance, the neutral atom, chlorine, contains 17 electrons. Therefore, we can write the configuration as
  • Similarly, Chloride ion or contains 18 electrons. Therefore, the single electron will occupy first the partially filled 3p orbital, filling it completely. Hence, we can write the configuration as
  • In case of Cations, the electron configuration will be drawn first by eliminating electron from the outermost p sub-shell, then from s and d orbital as well. For example, the electron configuration of calcium is . However, the calcium ion or has two less electrons. Hence the configuration of it will be .
  • Similarly, you can write the orbital configuration of several other atoms as well to get accustomed to the methods.
  • Thus, electron configuration plays a vital role in determining the behavior or chemical properties of an element, starting from the simplest molecules like helium and hydrogen to most complex ones that are seen in human body.

Stability of Completely Filled and Half-Filled Orbitals

Almost all the elements follow the same trend for writing electronic configuration. Sometimes when two sub-shells differ in the energies, an electron from the lower energy moves to higher energy.

This is because of two reasons:

  • Symmetrical distribution: As everyone knows that symmetry leads to stability. The orbitals in which the sub-shell is exactly half-filled or completely filled are more stable because of the symmetrical distribution of electrons.
  • Exchange energy: The electrons which are there in degenerate orbitals have a parallel spin and tend to exchange their position. Exchange energy is nothing but the energy released during this process. When the orbitals are half-filled or completely filled then the number of exchanges is maximum. Therefore, its stability is maximum.


Which Electron Configuration is the Most Stable?


  • It is observed that the noble gases have the most stable orbital configuration.
  • The reason behind it is their valence shell is completely filled. In the case of helium, the two valence electrons exist in 1s sub – level, and other eight electrons are in the s and p sub – shells.

How Electron is Arranged in an Orbital?


  • The nucleus of an atom is surrounded by orbitals, and on these orbitals, electrons are arranged.
  • However, the electrons closest to the nucleus contain lowest energy, and the furthest ones have the highest energy.
  • Also, the electrons primarily move within orbitals or sub-shells of an atom.

How Many Electrons Are There in a Shell?


  • Each shell is filled with a fixed number of electrons. It is determined by a simple formula, where for nth shell, the maximum number of electrons will be .
  • For example, the first shell holds a maximum of 2 electrons, and for second and third ones, the number goes up to 8 and 18, respectively.

What Does Orbitals S P D F Mean?


Orbital names refer to the group lines originally to the spectra of alkali metals. Thereby these groups of lines s p d f mean sharp, principle, diffuse and fundamental, respectively.

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