Chemical properties of the group 1 elements

Atoms of group 1 elements all have one electron in their outer shell. This means that the alkali metals all have similar chemical properties.

Reaction with moist air

Group 1 elements react with moist air. They are stored in oil to stop air and water vapour coming into contact with them. Moist air reacts with potassium to form potassium oxide. This creates a layer over the surface of the metal.

Reactions with water

The alkali metals react with water to produce a metal hydroxide and hydrogen. For example, sodium reacts with water:

sodium + water → sodium hydroxide + hydrogen

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Sodium hydroxide is an alkali. It is a base that dissolves in water to form an alkaline solution. This solution:

Question

Write the word equation and balanced chemical equation for the reaction of potassium with water.

potassium + water → potassium hydroxide + hydrogen

2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)

Reactions compared

The table shows the main observations when lithium, sodium and potassium are added to water.

These observations may be used to find a pattern in the reactivity of the group 1 elements.

These observations show that the reactivity of these metals increases going down the group.

Group 1 elementObservations
Lithium, LiFizzes steadily, and slowly becomes smaller until it has all reacted
Sodium, NaMelts to form a ball, fizzes rapidly, and quickly becomes smaller until it disappears
Potassium, KQuickly melts to form a ball, burns violently with sparks and a lilac flame, and reacts rapidly, often with a small explosion

Example

The reaction of potassium with water gives a lilac flame
The reaction of potassium with water gives a lilac flame

Rubidium is placed below potassium in group 1. Predict what is seen when rubidium is added to water.

Rubidium should melt very quickly. It should burn very violently, and react almost instantly with an explosion.

Reaction with chlorine

The group 1 metals all react with chlorine to produce chlorides. The chlorides are all white solids at room temperature, and dissolve in water to make a neutral solution.

Sodium + chlorine → sodium chloride

2Na(s) + Cl2(g) → 2NaCl(s)

The reactions get more vigorous going down the group.