Electronic Configurations of Atoms

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The distribution of electrons in different orbitals is known as electronic configuration of the atom. The orbitals are indicated by a box (square or circular) and electrons are indicated by arrows. An empty square will mean an empty orbital, while a single electron will be indicated by drawing one arrow in the square and two electrons will be shown by a pair of arrows with their heads in the reverse direction. The direction of the arrow gives the orientation of its spin.

Alternatively, electronic configuration is expressed by indicating the principal quantum number and its respective orbital along with the number of electrons present in it. For e.g., the notation 3p_x¹ indicates that there is one electron in p orbital of third principal shell.

fig 1.6 - Energy level diagram for a multi-electron atom

The energy level diagram for a multi-electron atom is as shown above.

The filling of orbitals is governed by the following rules:

1) Aufbau principle

2) Pauli's exclusion principle

3) Hund's rule of maximum multiplicity.