2.2 Group 2, the alkaline earth metals

AS Paper 1 A Level Papers 1 and 3

Explain how the atomic radius changes down group 2.

The atomic radius increases down group 2.
Extra electron shells are added.

Explain how the first ionisation energy changes down group 2.

The first ionisation energy decreases down group 2.
Each element down group 2 has an extra electron shell compared to the one above, so there is more shielding.
The outer electron is also further away from the nucleus.
There is less attraction between the nucleus and outer electron.

Explain the melting point of the group 2 elements in terms of their structure and bonding.

The group 2 elements have giant metallic structures, with strong electrostatic attraction between the positive ions and the sea of delocalised electrons.
This gives them very high melting points.

Explain how the melting point changes down group 2.

The melting point decreases down group 2.
Ionic radius increases, the same number of delocalised electrons per atom, and the same charge on each ion.
Delocalised electrons are further from the nucleus so there is less attraction between them.

Why is there a drop in the melting point for magnesium?

Magnesium has a different crystal structure, where the metallic ions are arranged differently.

What happens to the group 2 elements when they react?

When group 2 elements react they are oxidised from a state of 0 to +2, forming M²⁺ ions.

What is produced when the group 2 elements react with water?

When the group 2 elements react with water they produce a metal hydroxide and hydrogen gas.

Explain how the reactivity of the group 2 elements changes down the group.

The reactivity of the group 2 elements increases down the group because the first AND second ionisation energies decrease.

What is magnesium used for?

Magnesium is used to extract titanium from TiCl₄.

Describe the process where magnesium is used to extract titanium.

Titanium oxide is converted to titanium chloride by heating it with carbon in a stream of chlorine gas.
The titanium chloride is purified by fractional distillation and is reduced by magnesium in a furnace at almost 1000°C

Give the equation for the extraction of titanium from TiCl₄.

TiCl_4(g) + 2Mg_(l) —> Ti_(s) + 2MgCl_2(l)

Describe how the relative solubilities of the hydroxides of the group 2 elements water change down the group.

The relative solubilities of the hydroxides of the group 2 elements water increases down the group.
Mg(OH)₂ is sparingly soluble.

Describe the use of Mg(OH)₂ in medicine.

In medicine, magnesium hydroxide is used in some indigestion tablets as an antacid.
This neutralises excess stomach acid.

Describe the use of Ca(OH)₂ in agriculture.

In agriculture, calcium hydroxide is used to neutralise acid soils.

Describe a use of CaO or CaCO₃.

Calcium oxide or calcium carbonate can be used to remove sulfur dioxide from flue gases.
The CaO / CaCO₃ is mixed with water to make a slurry and this is sprayed on the flue gases.

Write an equation for the reaction between CaO and SO₂.

CaO_(s) + 2H₂O_(l) + SO_2(g) → CaSO_3(s) + 2H₂O_(l)

Write an equation for the reaction between CaCO₃ and SO₂.

CaCO_3(s) + 2H₂O_(l) + SO_2(g) → CaSO_3(s) + 2H₂O_(l) + CO_2(g)

Describe how the relative solubilities of the sulfates of the group 2 elements in water change down the group.

The relative solubilities of the sulfates of the group 2 elements in water decrease down the group.
BaSO₄ is insoluble.

Describe the use of acidified BaCl₂ solution.

An acidified BaCl₂ solution is used to test for sulfate ions.
A white precipitate of is BaSO₄ made.

Why is BaCl₂ solution used to test for sulfate ions?
Why it is acidified?

Barium chloride solution is used because barium sulfate is insoluble, so a precipitate is made.
The barium chloride solution is acidified with hydrochloric acid to remove any sulfites or carbonates, which would also produce a white precipitate.

Describe a use of BaSO₄ in medicine.

In medicine, barium sulfate is used in a barium meal.
Barium sulfate is opaque to X-rays, it blocks the X-rays.