Review of Electron Configurations

Brief Instructions:

An electron configuration is a method of indicating the arrangement of electrons about a nucleus. A typical electron configuration consists of numbers, letters, and superscripts with the following format:

1. The coefficient is the first number indicates the energy level.

2. The lowercase letter indicates the type of orbital (s, p, d, or f).

3. A superscript indicates the number of electrons in the orbital.

Example: 1s² means that there are two electrons in the ‘s’ orbital of the first energy level. The element is helium (He).

To write a longhand electron configuration:

1. Begin on the upper-left-most position of the periodic table (1st energy level, s orbital) and begin moving across and down the table.

2. Use the Aufbau principle to fill in electrons in each orbital. The Aufbau process requires that electrons fill the lowest energy orbitals first. In another words, atoms are built from the ground upwards.

3. The sum of the superscripts should equal the total number of electrons.

Example: Mg 1s² 2s² 2p⁶ 3s²