Question

explain why the energetically higher lying ns orbitals are filled with 2 electrons in transition elements before the lower lying (n-1) d orbitals are filled.

Answer 1

Ans :

The electrons are filled in the orbitals of an atom in accordance to the aufbau rule.

According to this rule , the electrons are filled in the lower energetic orbitals first and then into higher energy orbitals.

This energy can be predicted by the sum of n and l ( principle and azimuthal quantum number).

For example , we fill 4s orbital first before 3d , the energy value of 4s = 4 + 0 = 4 and that of 3d is 3 + 2 = 5.

Since energy comes out lesser for 4s which is basically ns orbital and more for 3d (n-1) d orbital , so the former is filled up first.