3.1.1.3 - Electron Configuration

Define ionisation energy

What is the general trend along period 3 for ionisation energy and why does this occur?

Elements increase in ionisation energy due to:

• Greater nuclear charge

• Smaller atomic radius

What are the two elements that deviate from the general trend along period 3?

• Aluminium

• Sulfur

Why do the two elements deviate from the general trend along period 3?

• Al - Aluminium's outer electron is in a 3p orbital rather than a 3s. The 3p electron is slightly more distant from the nucleus than the 3s therefore requires less energy to remove

• S - Sulfur’s outer electron is being removed from a pair in an orbital. The repulsion between the two electrons in the same orbital means that the electron is easier to remove

• Element - Phosphorus (1)

• Explanation - Large jump in ionisation energy for the 6^th ionisation energy (1) due to the electron being removed from a shell closer to the nucleus therefore requiring more energy to remove (1)