Electron Configurations

Section 3 Electron Configurations

The order of increasing energy for atomic sub levels is show on the vertical axis on page 111 of the chemistry book. Each individual box represents an orbital.

Rules Governing Electron Configurations

• According to the Aufbau principle, an electron occupies the lowest-energy orbital that can receive it.
• According to the Pauli exclusive principle, no two electrons in the same atom can have the same set for four quantum numbers.
• According to Hund's rule, orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin state.

Representing Electron Configurations

Orbital Notation

• An occupied orbital is represented by a line, with the orbital's name written underneath the line.
• An orbital containing one electron is represented as one arrow pointing in the upright position with a line under it.

• An orbital containing two electrons are represented as one arrow pointing in the upright position(North) and one arrow pointing in the down position(South) with a single line under both.

• The lines are labeled with the principal quantum number and sub level letter. For example, the orbital notation for helium is written as the symbol He to the left of an arrow pointing North and an arrow pointing South with an single line under it having (1s).

P.S. The arrows with (1s) written under it is written similar to a fraction having (He) as the whole number.