ELECTRONIC CONFIGURATION: The distribution or arrangement of electrons around the nucleus in various shells and sub shells according to their increasing energy is called electronic configuration.

Explanation: The electrons fill the shells in order of their increasing energy that is lower energy level is occupied first then the higher energy level and so on.

The electrons revolve around the nucleus in different energy levels or shells according to their increasing energy. Energy levels are represented by “n” values, and n= 1, 2, 3 . . . They are designated by alphabets K, L, M , … . K shell is closest to the nucleus, the energy of the shells increases from K -shell onwards. n = n = n = n =

  • K-shell= 1st energy level.
  • L-shell= 2nd energy.
  • M-shell= 3rd energy level.
  • N-shell= 4th energy level


n Value Shell Subshell
1 K Only s
2 L s, p
3 M s, p, d
4 N s, p, d, f


A shell or orbit also consists of subshells or orbitals. The number of sub shells in a shell is equal to its n – value. Subshells may be of four types. s ,p ,d and f.

1st shell that is K shell has only 1 subshell s, 2nd shell that is L shell has 2 subshells s and p, 3rd shell that is M shell has 3 subshells s,p and d, 4th shell that is N shell has 4 subshells s,p,d and f.

The maximum capacity of shells to accommodate the electrons is as follow K shell can accommodate 2 electrons, L shell can accommodate 8 electrons, M shell can accommodate 18 electrons, N shell can accommodate 32 electrons. The order of filling of electrons in sub shells is given by s,p,d,f.

S subshell can accommodate 2 electrons.

P subshell can accommodate 6 electrons.

d subshell can accommodate 10 electrons.

f subshell can accommodate 14 electrons.


Requirements for electronic configuration : Following are the requirements for electronic configuration.

(1) Find atomic number of the required atom: To configure electrons in an atom’s shells and sub shells. First you have to know the atomic number of the atom which is the number of protons in the nucleus of an atom. It is also the number of neutrons in the shells, if the atom is neutral.

(2) Determine the charge on the atom: uncharged atoms have number of electrons equal to the atomic number. If you have a charged atom. Add one electron for each negative charge and subtract one electron for each positive charge. For example a magnesium atom with a +2 charge (MG2+) means that it has lost 2 electrons. Neutral Mg atom has 12 electrons. Now there are 10 electrons in magnesium. So electronic configuration of neutral and charged atoms are different.

(3) Standard electronic configuration: You also have to know about standard electronic configuration that is 1S2, 2S2, 2P6, 3S2, 3P6, 4S2, 3d10, 4p6, 5S2, 4d10, 5p6, 6S2, 4f14, 5d10.

(4) Number of electrons in each orbital: keep in mind that each orbital accommodate fixed number of maximum electrons. Each S orbital accommodate 2 electrons, p accommodate 6, d accommodate 10 while f accommodate 14 electrons.

(5) Number of sub shells (orbitals) ; energy level 1 has only one subshell, energy level has 2 sub shells, energy level 3 has three sub shells, and so on.

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