Chapter 9: Group 2, the alkaline earth metals

Why are they called the alkaline earth metals?

Their oxides and hydroxides are alkaline

How do the group 2 metals compare to the group 1 metals?

- Harder
- Less reactive
- much higher melting points
- also not found in nature in elemental form

Why do group 2 metals have high melting points?

They form giant metallic structures

How does atomic radius change down the group?

increases (more electron shells)

How does first IE change down the group?

Decreases

Why does first IE decrease down the group?

- Atoms get bigger
- More shielding
- Therefore weaker attraction from nucleus and outer electron more easily lost

What is the general trend for melting point down the group?

Decrease

Why does melting point generally decrease down the group?

- Weaker metallic bonding because sea of delocalised electrons further from positive nuclei
- as metal ions are bigger
- so lower melting points

How does each element react with water?

Beryllium - very unreactive
Mg - slightly reactive
Ca, Strontium, Barium - all react with increasing vigour

How does magnesium react with steam?

Forms an alkaline oxide and hydrogen
Mg (s) + H₂O (g) → MgO (s) + H₂ (g)

How does solubility of the hydroxides change down the group?

Get more soluble as you go down the group
Mg(OH)₂ - almost insoluble
Ca(OH)₂ - sparingly solutble
Sr(OH)₂ - more soluble
Ba(OH)₂ - dissolves to produce strongly alkaline solution

How is magnesium hydroxide Mg(OH)₂ used?

As a medicine to combat indigestion

How is calcium hydroxide Ca(OH)₂ used?

Used in agriculture to optimise pH of the soil and in lime water

How is calcium oxide made?

Made by heating calcium carbonate until it decomposes
CaCO₃ (s) → CaO (s) + CO₂

What is calcium oxide used for? What is the process known as?

Used to remove SO₂ from the flue gases from power stations. Known as flue gas desulfurisation.

What does CaO react with SO₂ to form?

Calcium sulfite CaSO₂

What are flue gases?

A mixture of gases produced by the burning of fuels in power stations

What other compound can also be used to remove sulphur dioxide from flue gases?

CaCO₃

How does the solubility of the group 2 sulphates change as you descend the group?

They get less soluble as you descend the group

How is barium sulfate BaSO₄ used?

Used in barium 'meals' in X-rays

Why is barium sulfate used for X-rays?

It is insoluble and outlines the gut. It is harmless to humans

How can you test for sulfate ions?

1. Acidify the solution with either nitric acid or hydrochloric acid
2. Add barium chloride
3. If a sulfate is present, a white precipitate will be formed

What can be used in the extracted of titanium from titanium chloride?

Magnesium

When testing for sulphates, why is the solution first acidified?

Both sulfites and sulfates produce a white precipitate with BaCl₂. With sulphites, the precipitate dissolves in acid.