How does ionization energy relate to a metal's reactivity?

Ionisation energy and a metal's reactivity are inversely related; the lower the ionisation energy, the higher the reactivity.

Ionisation energy is the energy required to remove an electron from an atom or ion. It is a measure of how tightly an atom holds onto its electrons. In the case of metals, they tend to lose electrons to form positive ions, a process known as oxidation. The ease with which a metal can lose its electrons (and thus oxidise) is a key factor in determining its reactivity.

Metals with low ionisation energies can lose their outermost electrons with relative ease. This is because the attractive force between the nucleus and the outermost electrons is weaker, making it easier for these electrons to be removed. As a result, these metals are more likely to react with other substances, making them more reactive. For example, alkali metals like sodium and potassium have very low ionisation energies and are highly reactive.

On the other hand, metals with high ionisation energies hold onto their electrons more tightly. The attractive force between the nucleus and the outermost electrons is stronger, making it more difficult for these electrons to be removed. Consequently, these metals are less likely to react with other substances, making them less reactive. For example, transition metals like gold and platinum have high ionisation energies and are less reactive.

In summary, the reactivity of a metal is largely determined by its ionisation energy. The lower the ionisation energy, the more easily a metal can lose its electrons and react with other substances, making it more reactive. Conversely, the higher the ionisation energy, the more difficult it is for a metal to lose its electrons and react with other substances, making it less reactive. This relationship is a fundamental concept in understanding the reactivity series of metals, which ranks metals in order of their reactivity.