CHEMISTRY GROUP 2

Y1

Trend in atomic radius down group 2

As you go down the group, atomic radius increases as the outer electrons are at a higher energy level and experience more shielding.

This weakens the attraction between the nucleus and valence electrons.

Trend in 1st ionisation energy down group 2

As you go down the group, first ionisation energy decreases as atomic radius and shielding increase.

This means the outer shell electron is further from and less attracted to the nucleus, so less energy is required to remove it.

Trend in melting points down group 2

As you go down the group, melting points decrease as the delocalised electrons are further from the nucleus and charge density decreases.

This weakens the attraction between the ions and delocalised electrons, so less energy is required to overcome it.

Reactions of group 2 metals with water

Produce a metal hydroxide and hydrogen

M _(s) + H₂O_(l) —> M(OH)_{2 (aq)} + H_{2 (g)}

What do we observe when a group 2 metal reacts with water?

• Effervescence (H₂ gas).

• Solid metal gets smaller until it disappears.

Reaction of magnesium with water

Very slowly in cold water but vigorously with steam.

The magnesium then burns bright with a white flame.

Reaction with steam produces magnesium oxide but water produces magnesium hydroxide

As you go down group 2, the solubility of hydroxides...

Increases

Magnesium hydroxide is...

Sparingly soluble.

Magnesium hydroxide appearance + use

White solid precipitate

pH > 7 so we can use it as an antacid. It neutralises excess stomach acid.

Calcium hydroxide use

To neutralise acidic fields as it raises the pH of the soil.

As you go down group 2, the solubility of sulphates...

Decreases

Barium sulphate uses

Barium ions are extremely toxic, but barium sulphate is insoluble, so it can be safely consumed as it cannot be absorbed into the blood.

X-rays cannot pass through barium compounds, meaning barium sulphate meals can be used as medical tracers to image internal tissues and organs.

Test for sulphate ions

Add acidified barium chloride

Positive result: white precipitate (barium sulphate) forms

Why is the barium chloride acidified?

It removes carbonate impurities to prevent the formation of a barium carbonate precipitate.

Uses of calcium oxide and calcium carbonate

To remove sulphur dioxide from waste emissions of burning fossil fuels.

This is known as flue gas desulphurisation.

Calcium oxide: flue gas desulphurisation equation

2CaO + O₂ + 2SO₂ → 2CaSO₄

Calcium carbonate: flue gas desulphurisation equation

2CaCO₃ + O₂ + 2SO₂ → 2CaSO₄ + 2CO₂

Use of magnesium

Used in the extraction of titanium from its oxide ore, rutile.

It displaces the titanium.

Titanium extraction equations

TiO₂ + 2C + 2Cl2 → TiCl₄ + 2CO

TiCl₄ + 2Mg → 2MgCl₂ + Ti