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Reactions with oxygen

The group 1 elements react with oxygen from the air to make metal oxides.

At room temperature, oxygen reacts with the surface of the metal. This forms a white oxide, which covers the surface. The metal below the surface does not react.

The alkali metals burn vigorously when heated and placed in a gas jar of oxygen. The oxide forms as white smoke.

For example:

sodium + oxygen → sodium oxide

4Na(s) + O₂(g) → 2Na₂O(s)

The reactivity of the group 1 elements increases down the group, so their reactions with oxygen get more vigorous.

Reactions with chlorine

The group 1 elements react vigorously with chlorine. The products of the reactions are chlorides. At room temperature the chlorides are white solids. They dissolve in water to form colourless solutions. For example:

sodium + chlorine → sodium chloride

2Na(s) + Cl₂(g) → 2NaCl(s)

The reactions with chlorine get more vigorous going down the group.

Explaining the trend in reactivity

When a group 1 element takes part in a reaction, each of its atoms loses its outer electron to form a positively charged ion. The more easily the ions form, the more reactive the metal.

Going down group 1:

• the atoms become larger
• the outer electron becomes further from the nucleus
• the force of attraction between the nucleus and the outer electron decreases
• the outer electron is lost more easily