Trends of Ionisation
Chemistry: AQA A Level, topic 1.1.8
Trends in First Ionisation Energies
First ionisation energies change in a predictable way throughout the periodic table.
Trend across a period
- First ionisation energy increases across a period.
- This is because the atomic radius decreases. Proton number increases across a period, so electrons are more attracted to the nucleus.
- The electron is closer to the nucleus, and so experiences a greater attraction.
- Nuclear charge increases across a period.
Trend down a group
- First ionisation energy decreases down a group.
- This is because the atomic radius increases.
- The electron is further from the nucleus, and so experiences lower attraction.
- There are also more electrons between the nucleus and the outer electrons.
- This means the outer electrons experience greater shielding from the nucleus.
- This also provides evidence for the existence of shells.
Test yourself on Trends of Ionisation
How does ionisation energy vary within the periodic table?
How does ionisation energy vary within the periodic table?
Why does ionisation energy increase across a period?