Ground states subshell electronic structure

The magnetic moment of an atom is due entirely to partially filled subshells and unpaired spins. The completed subshells do not contribute to the permanent magnetic moment of an atom. In this connection we might remark that most molecules have an even number of electrons whose spins in the ground state are all paired. Also the subshells are usually complete so that there is no contribution to the magnetic moment from the orbital motion. It is unusual for a molecule to have a permanent magnetic moment the possession of a permanent magnetic moment is an important key to the electronic structure of the molecule. 

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