Group 1 - chemical reactions with oxygen and chlorine

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.

Question

Predict which becomes white more quickly on exposure to air - a piece of rubidium, or a piece of lithium. Explain your answer.

The rubidium becomes white more quickly. This is because rubidium is below lithium in group 1, so rubidium is more reactive.

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.

Question

Write a balanced equation for the reaction of potassium with chlorine.

2K(s) + Cl2(g) → 2KCl(s)

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
Table showing electronic structures of group 1 elements, lithium, sodium and potassium. Group 1 elements have similar properties and reactions as they all have one electron in their outer shell.