What is aufbau's principle

RULES OF WRITING ELECTRONIC CONFIGURATION:

          “It is the number of electrons in different orbitals. “

There are certain set of rules that are followed:

Aufbau principle: It states that in ground state of atom, the orbitals are filled in order of their increasing energies. That is electrons first occupy the lower energy orbital then higher energy orbitals are filled.

According to it:

1. The lower the value of n+l for an orbital, the lower is its energy and is filled first.

For example: Out of 2s and 2p ,2s is filled first as n+l for 2s, is 2+0=2 and for 2p it is 2+1=3. Therefore, 2s is filled first.

1. If two orbitals have same value of n+l , than the orbital with lower value of n is filled first.

For example: Out of 3p and 4s, n+l for both is 4 . Therefore, 3p is filled first as it possess lesser value of n.