Ionization Energy
Chemistry: IB Diploma Higher Level, topic 1.1.9
Ionization Energy
We see trends in ionization energy across the periods and down the groups of the periodic table.
Periodic trend
- Ionization energy increases along a period.
- This is because the electrostatic attraction of each electron to the nucleus increases.
- The attraction increases because the proton number increases.
Periodic example
- In Period 3, chlorine has a greater nuclear charge than sulfur because it has a greater proton number.
- So the electrostatic charge between electrons and the nucleus in chlorine will be greater.
- So the ionization energy is greater.
Group trend
- Ionization energy decreases down a group.
- This is because the outer electron is further from the nucleus down the group.
- The electrostatic attraction of the outer electron to the nucleus decreases down the group.
Group example
- In Group 2, magnesium is below beryllium.
- Magnesium fills up an extra electron shell than beryllium.
- This means an electron is further from the nucleus in magnesium and so the electrostatic attraction is less.
- So the ionization energy of magnesium is lower than beryllium.
Test yourself on Ionization Energy
Why does the distance between electrons and nuclei increase down a group?
Iodine is in Period 5 and chlorine is in Period 3. Which has a bigger radius?