Group 1 and Group 7

The group 1 elements (except hydrogen) are known as the alkali metals. The first three alkali metals are lithium, sodium and potassium. Out of these three, potassium is the biggest, so it is the most reactive.

When the alkali metals react with water, they all produce hydrogen and form an alkali metal hydroxide solution.

The halogens are the group 7 elements. These are all coloured non-metals.