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Group 2 Chemistry

Chemistry: AQA A Level, topic 3.2.1

Properties of Group 2 Metals

Elements in the same group have similar properties. Here, we shall look at the similarities between the properties of the Group 2 elements.

Atomic radius and ionisation energy

Atomic radius and ionisation energy

  • Atomic radius increases as you go down Group 2.
  • This is because each extra electron shell is further away.
  • Ionisation energy decreases as you go down Group 2.
  • This is because the outer electrons are further away and experience less attraction to the nucleus.
Melting point

Melting point

  • Melting points decrease as you go down Group 2.
  • This is because the ion cores have larger radii down the group.
  • The free electrons experience less attraction to the nuclei because of the larger radii.
  • The bonding is weaker, so the melting point is lower.
  • Magnesium has an anomalously low melting point.
  • This is because it has a different crystal structure to the rest of Group 2.
Reactions with water

Reactions 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.
Solubility of salts

Solubility of salts

  • The solubility of hydroxides increases as you go down Group 2.
  • Magnesium hydroxide is very insoluble. The phrase to use for this is 'sparingly soluble'.
  • The solubility of sulfates decreases as you go down Group 2.
  • Barium sulfate is completely insoluble.

Uses of Group 2 Compounds

Group 2 compounds have a number of uses in industry and society. Examples of these uses include:

Titanium extraction

Titanium extraction

  • The first step in the extraction process is converting titanium ore (TiO2) to titanium chloride (TiCl4) using chlorine gas and carbon.
  • The second step involves heating TiCl4 with magnesium metal at 1,000oC. The equation for this step is:
  • TiCl4(g) + 2Mg(l) →\rightarrow Ti(s) + 2MgCl2(l)
As bases to neutralise acids

As bases to neutralise acids

  • Calcium hydroxide (sometimes called slaked lime) and magnesium hydroxide are used to neutralise acids.
  • Calcium hydroxide is used to neutralise acidic soils in agriculture.
  • Magnesium hydroxide is used in indigestion tablets as an antacid that neutralises excess stomach acid.
In healthcare

In healthcare

  • 'Barium meals' (made of barium sulfate) are used in healthcare.
  • X-rays can detect solid materials like bones but aren't very good at detecting soft tissues.
  • 'Barium meals' are insoluble and reflect X-rays.
  • A barium meal coats the oesophagus, stomach, and intestines and makes the structure of them show up on X-rays.
Wet scrubbing

Wet scrubbing

  • Wet scrubbing is the process of removing SO2 from flue gases.
  • Flue gases come from chimneys and industrial waste.
  • CaO and CaCO3 are used to remove the SO2 from the gases.
  • This works because SO2 is acidic and the calcium compounds are bases.
  • The CaO is mixed with water and sprayed onto the gases.
  • The byproduct is calcium sulfite, CaSO3.

Test yourself on Group 2 Chemistry

  • Why is magnesium's melting point lower than expected?

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