Electrons Hund’s rule and

It has been found that electrons behave as if they spin on an axis, and only electrons spinning in opposite directions (indicated by t and ) can occupy the same orbital. This principle, known as the Pauli exclusion principle, explains why orbitals can contain a maximum of two electrons. Hund s rule and the Pauli exclusion principle can be combined Electrons will pair with other electrons in an orbital only if there is no empty orbital of the same energy available and if there is one electron with opposite spin already in the orbital. 

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