CBSE Class 11-science Answered

To find electronic configuration of atoms, you should know its atomic numbers.

For electronic configuration of elements, the most important thing that you should be aware of -

The order in which orbitals of different subshells are filled. We know that this order is determined by the (n + l) rule and is as follows:

Order for filling subshells: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 

where the number indicates the energy level and the letter indicates the subshell being filled.

Maximum number of electrons in each subshell: s=2, p=6, d=10, f=14 

A superscipt number after the letter of the subshell shows how many electrons occupy that subshell.

The helium atom has 2 electrons, both in the s subshell of the first energy level. 
Its sub-shell electron configuration is 1s²

The neon atom has 10 electrons. 
2 electrons in the s subshell of the first energy level: 1s² 
8 electrons in second energy level, made up of 2 electrons in an s subshell and 6 electrons in a p subshell: 2s² 2p⁶ 
Its subshell electron configuration is 1s² 2s² 2p⁶

The argon atom has 18 electrons. 
2 electrons in the s sub-shell of the first energy level: 1s² 
8 electrons in the second energy level made up of 2 electrons in an s subshell and 6 electrons in a p subshell: 2s² 2p⁶ 
8 electrons in the third energy level made up of 2 electrons in an s subshell and 6 electrons in a p subshell: 3s² 3p⁶ 
Its subshell electron configuration is: 1s² 2s² 2p⁶ 3s² 3p⁶

Table showing examples of electronic configuration of atoms and ions are as follows: