Reactivity of Alkaline Earth Metals
Applied Science: BTEC Level 3 National Extended Diploma, topic 1.2.10
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.
Trends in reactivity
- The reactivity of group 2 metals increases down the group.
- The ionisation energies needed decrease down the group because increased shielding from extra shells of electrons and a greater distance from the nucleus makes it easier to remove an outer electron.
- Both first and second ionisation energies decrease down the group. The second ionisation energy is greater than the first ionisation energy within an element.
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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
- 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
- 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 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
- 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
- Beryllium oxide does not react with water.
- Magnesium oxide reacts but very slowly.
Test yourself on Reactivity of Alkaline Earth Metals
Which of the following group 2 metals do NOT react with water?
Which of the following group 2 metals has the strongest reaction with water?
How do these group 2 oxides react with water?
Why is calcium hydroxide (slaked lime) used on soil for growing crops?