By Team Aakash Byju's
To write the electronic configuration of an element, identify the noble gas in the periodic table before the selected element.
The noble gases are helium, neon, argon, krypton, xenon and radon. We find them in the last column of the periodic table.
If you are writing the electronic configuration of sodium which is in the third, row we will use neon’s configuration which is in the second row.
The full electron configuration for sodium is 1s2 2s2 2p6 3s1 and that of neon is 1s2 2s2 2p6.
Thus, the electronic configuration of sodium can be written as [Ne]3s1.