how to find the electronic configuration …

Electron Configuration and Valence Electrons

Electron Configuration

The electrons in an atom fill up its atomic orbitals according to the Aufbau Principle; "Aufbau," in German, means "building up." The Aufbau Principle prescribes a few simple rules to determine the order atomic orbitals are filled with electrons:

1. Electrons always fill orbitals of lower energy first. 1<i>s</i> is filled before 2<i>s</i> , and2<i>s</i> before 2<i>p</i> .
2. If two electrons occupy the same orbital, they must have opposite spin, as required by the Pauli Exclusion Principle.
    
3. When electrons have to choose between two or more orbitals of the same energy, electrons prefer to go into different orbitals. As more electrons as added to the atom, these electrons tend to half-fill orbitals of the same energy before pairing with existing electrons to fill orbitals. This is known as Hund's Rule.