Ionization energy trend

atomic radius

Ionization energy trend

Ionization energy is defined as the amount of energy needed to eject a valence electron from an atom in the gas phase. It is measured in kJ/mol.

A valence electron is simply an electron located in the outermost energy level of an atom.

Ionization energy

Watch an interesting video here to see how ionization energy is measured. 

What is the ionization energy trend in the periodic table?

From the previous discussion, we know that going across a period in the periodic table, the atomic radius decreases (i.e. atoms get smaller).
Ionization trend

  • As the atomic radius decreases, the nucleus is able to pull the valence electrons closer.
  • This means more energy is required to remove the valence electrons that are now more tightly held.
  • Therefore the ionization energy increases when atomic radius decreases.

Ionization energy increases from left to right across the periodic table as atoms get smaller.

Ionization trend

Can you explain the ionization trend within a group?

  • The atomic radius gets larger going down a group.
  • This is because there are more layers of core electrons.
  • The core electrons reduce the effectiveness of the nucleus attraction on the valence electrons.
  • Therefore the valence electrons are less tightly held and are able to move farther from the nucleus.
  • Since the valence electrons are less tightly held by the nucleus, they are easier to be removed, and hence the ionization decreases.

Generally, ionization energy reduces down a group in the periodic table as atoms get larger.

(Atomic radius trend)

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