Page 22 - Electronic Configuration

4s is more stable than 3d orbital  in terms of energy.

However, as soon as the electron occupy the 3d

orbitals, the 4s electrons are repelled to higher energy.

EXAMPLE: Titanium, Ti (Z = 22)

2
2
6
6
2
Electron configuration: 1s 2s 2p 3s 3p 4s 3d 2
2
(by applying Aubau principle)

2
2
6
2
Electron configuration: 1s 2s 2p 3s 3p 3d 4s 2
6
2
(due to energy level after repulsion)

Note: Both configurations can be used!