AS-Level Group 2 Metals

  • Reactivity of group 2 metals increases going down the group.

  • Down the group, outer electrons are held less tightly due to increased inner electron shielding, so they are easier to lose, making the metals more reactive.

  • Group 2 metals form metal hydroxides when they react with water.

    • Beryllium is not reactive enough to form a hydroxide.

    • Magnesium does react with water but only slowly.

  • The solubility of group 2 metal hydroxides increases down the group.

    • The solutions are more alkaline as more hydroxide ions are released into solutions (pH of metal hydroxide solutions increases down the group).

  • The solubility of group 2 metal sulfates decreases down the group, with barium sulfate being completely insoluble.

QUICK NOTES

Group 2 Metal Reactions

 

As you go down group 2, atoms lose their outer electrons more readily (due to increased inner electron shielding) and so form positive ions more easily. This means as you go down the group, atoms become more likely to react –their reactivity increases.

 

Reactions with water

 

The trend in reactivity down group 2 can be observed with the reactions of group 2 metals with water.

 

 

 

 

 

 

 

 

 

 

 

 

 

Mg(s) + 2H O(l) → Mg(OH) (aq) + H (g)

 

Magnesium with water is a very slow reaction, producing Mg(OH) (aq) and hydrogen gas.

However, reacting magnesium with steam causes magnesium oxide to be formed, in a much faster reaction.

 

Mg(s) + H O(g) → MgO(s) + H (g)

 

Below magnesium, the group 2 metals react vigorously with water, each producing metal hydroxides.

Ca(s) + 2H O(l) → Ca(OH) (aq) + H (g)

 

Solubility of hydroxides

 

The metal hydroxides produced from reacting group 2 metals with water (see above), dissolve differently in solution. How well a substance dissolves in water is described as its solubility. A substance with a high solubility will readily dissolve in water, a substance with a low solubility will not dissolve easily in water.

 

For group 2 hydroxides, solubility in water increases as you go down the group.

 

 

 

Metal hydroxides are ionic compounds, which when dissolved in water, ‘split’ into the positive ions (anions) and positive ions (cations) that make up the substance.


For example, Ba(OH) (s) in water dissolves to form Ba  (aq) and 2OH⁻(aq) ions.

 

OH⁻ ions can accept protons and act as bases. So, when a metal hydroxide dissolves in water, an alkaline solution is formed as it contains OH⁻ ions.

 

The group 2 hydroxides dissolve more readily as you go down the group, causing the solutions formed to become more alkaline as there are more OH⁻ ions released by the hydroxide dissolving.

 

The ability of group 2 hydroxides to form alkaline solutions can be very useful.

 

For example:

Lime (Ca(OH) ) is widely used in agriculture; it is applied to fields to help raise the pH of acidic soil to make growing conditions more favourable for some crops.

 

Magnesium hydroxide, Mg(OH) , is commonly used as indigestion tablets to help neutralise excess stomach acid.

 

 

Group 2 Sulphates

 

Group 2 metal sulphates are ionic compounds, made from a group 2 metal ion (M  ) and a sulphate ion (SO  ).

The solubility of group 2 metal sulphates decreases as you go down the group. MgSO is highly soluble, but Ba(SO ) is insoluble.

 

 

 

The insolubility of barium sulphate can be very helpful in chemistry; it forms the basis of a test to identify sulphate ions in solution.

 

A barium salt solution (commonly BaCl (aq)) is added to a solution (with dilute nitric acid) that may contain sulphate ions.  If sulphate ions are present insoluble Ba(SO ) will be formed, which can be identified as a white precipitate.

 

Barium sulphate is also used in radiography in medicine. Being a metal, barium shows up well in an x-ray, but it is highly toxic when ingested. However, because barium sulphate is insoluble, the barium is ‘trapped’ in the sulphate compound and cannot do any damage to a patient’s body.  A patient can ingest barium sulphate, and when x-rayed, we can see where the barium sulphate has travelled in the patient’s body. This can help identify digestive disorders and irregularities.

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