Ionisation energy and what controls it

4 minAS Level1.4.11.4.21.4.51.4.6

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end you can define first ionisation energy, write equations for first, second and later ionisation energies, and explain the four factors that control their size.

Definition

First ionisation energy, IE

The energy needed to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.

As an equation

For sodium:

$\text{Na(g)} \rightarrow \text{Na}^{+}\text{(g)} + \text{e}^{-} \qquad \text{first IE} = +496\ \text{kJ mol}^{-1}$

Both the atom and the ion have the state symbol (g).
Ionisation energies are always positive: removing an electron always takes energy.
Units: $\text{kJ mol}^{-1}$ , because it's per mole.

Quick check

DefinitionQuestion 1 · Recall

Define the first ionisation energy of an element.

CalculateQuestion 2 · Apply

The first ionisation energy of sodium is $496\ \text{kJ mol}^{-1}$ . How much energy is needed to convert 0.25 mol of gaseous sodium atoms into $\text{Na}^{+}\text{(g)}$ ions?

Answer the 2 questions above to continue.

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