1.2.10

Reactivity of Alkaline Earth Metals

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Reactivity of Group 2 Metals

The reactivity of group 2 metals increases down the group. This can be illustrated by their reactions with oxygen, water, and dilute acids.

Reaction with oxygen

Reaction with oxygen

  • Group 2 elements react with oxygen in the air to form metal oxides, For example:
    • 2Mg + O2 → 2MgO
  • The elements react more readily with oxygen down the group because of the decrease in ionisation energies.
Reaction with water

Reaction with water

  • Group 2 metals react with water to form metal hydroxides. For example:
    • Mg + 2H2O → Mg(OH)2 + H2
  • Reactivity increases as you go down Group 2. This is because the lower elements have lower ionisation energies.
    • Beryllium is an exception. If beryllium were to lose two electrons it would be tiny and have a very high charge density. This would make it unstable and so beryllium doesn't react with water.
Reaction with dilute acids

Reaction with dilute acids

  • Group 2 metals react with dilute acids to produce a salt and hydrogen. For example:
    • Ca + H2SO4 → CaSO4 + H2
  • Reactivity increases down the group because of the decrease in ionisation energies.
  • The salts produced become less soluble as you go down the group.

Group 2 Oxides Reacting with Water

Group 2 oxides react with water to form metal hydroxides.

Group 2 oxides and water

Group 2 oxides and water

  • Group 2 oxides steadily react with water.
  • The reaction produces a metal hydroxide salt. The salt dissociates into metal ions and hydroxide ions, giving the solution an alkaline pH.
Solubility down the group

Solubility down the group

  • Group 2 hydroxides become more soluble down the group.
  • This means that the solutions become more strongly alkaline the further down Group 2 you go.
Exceptions to the rule

Exceptions to the rule

  • Beryllium oxide does not react with water.
  • Magnesium oxide reacts but very slowly.
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