Rules to write the electronic configuration :
Electrons complete orbitals in a way to reduce the energy of the atom. Therefore, the electrons in an atom complete the principal energy levels in order of rising energy (the electrons are getting distant from the nucleus). The order of levels filled appearances like the following
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, and 7p
One way to recognise this pattern, apparently the simplest, is to refer to the periodic table and remember where each orbital block drops to rationally understand this pattern. Different way is to make a table like the one below and use vertical lines to determine which subshells resemble with each other.
- S block: The S obstruct in the periodic table of components known as gatherings 1 and 2. There is a limit of two electrons that can possess the s orbital.
- P Block: The P square contains group of 13, 14, 15, 16, 17, and 18, except for Helium.
- D Block: The D block elements are found in groups 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 of the periodic table.