The Group 1 elements have similar properties because of the electronic structure of their atoms – they all have one electron in their outer shell.

Explaining trends [Higher tier only]

In a reaction, an atom of a Group 1 element will form an ion with a single positive charge. For example, for sodium forming a sodium ion:

Na → Na⁺ + e^–

A change like this, where an electron is lost, is an example of oxidation.

The ions formed have a stable electronic structure, like a noble gas from Group 0.

The reactivity of Group 1 elements increases as you go down the group because:

• the atoms get larger
• the outer electron gets further from the nucleus
• the attraction between the nucleus and outer electron gets weaker – so the electron is more easily lost