Group 2

Group 2 elements are known as the alkaline earth metals.

They include: Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba).
They all have two electrons in their outer s-subshell (configuration ends in ns² ).

They form ions by losing two electrons. They are oxidised themselves and therefore act as reducing agents.

Definitions:

First ionisation energy: The energy required to remove one mole of electrons from one mole of gaseous atoms.
Atomic radius: The average distance between the nucleus of an atom and its outermost electron shell.

Group 2 metals show clear trends down the group:

Atomic Radius

Atomic radius increases down the group:
- Each successive element has an extra electron shell.
- A greater distance between the nucleus and the outer electrons.
- More shielding of nuclear charge.

First Ionisation Energy

Decreases down the group because:
- Increased atomic radius.
- Increased shielding.
- Weaker electrostatic attraction between the nucleus and the outermost electrons.

Trends in Melting Points

Generally decreases down the group.
- Metallic bonding weakens as ion size increases.
- This results in a larger distance between the charged metal ion and delocalised electrons, and thus a weaker attractive force.

Trends in Melting Points

Group 2 metals react with water to form a metal hydroxide and hydrogen:

(M = Group 2 element)

Notes:

Note – for the reaction between magnesium and steam, state symbols are typically expected.

The table below highlights the reactions of group 2 elements with water:

Element	Reaction	Equation	Observation
Mg (cold water)	Slow	Mg + 2H₂O → Mg(OH)₂ + H₂	Few bubbles
Mg (steam)	Fast	Mg + H₂O (g) → MgO + H₂	White solid, bright light
Ca	Moderate	Ca + 2H₂O → Ca(OH)₂ + H₂	Effervescence, white ppt
Sr	Fast	Sr + 2H₂O → Sr(OH)₂ + H₂	More vigorous
Ba	Very fast	Ba + 2H₂O → Ba(OH)₂ + H₂	Rapid bubbling

Solubility increases down the group:
- : sparingly soluble
- : slightly soluble
- and : increasingly soluble
Uses of Group 2 hydroxides
- : Used as an antacid to neutralise stomach acid.
- : Used in agriculture to neutralise acidic soils.

Solubility of Group 2 Hydroxides

Decreases down the group:
- : Soluble
- : Slightly soluble
- : Insoluble

Solubility of Group 2 Sulfates

Uses
- Barium sulfate, being insoluble, makes it useful in medicine as X-ray ‘barium meals’. It lines the digestive tract and absorbs X-ray radiation allowing outlines of organs to be visualised. Although ions are toxic, as barium sulfate is insoluble, the ions are not absorbed into the blood
- Barium chloride is used as a test for sulfate ions as it reacts to form barium sulfate, a white precipitate.

Titanium is extracted from TiCl₄ using magnesium:

Equation:

This is a redox reaction in which Mg reduces Ti⁴⁺ to Ti. The Mg is oxidised from 0 to +2.

Removing SO₂ from Flue Gases:

SO₂ released when coal with sulfur impurities is burned in power stations.
If SO₂ is released into the atmosphere, it will dissolve in clouds/rainwater producing acid rain
CaO or CaCO₃ is used to remove the in the desulfurisation of flue gases in power stations

Example equations:

CaO + SO₂ → CaSO₃

CaCO₃ + SO₂ → CaSO₃ + CO₂

Uses and Reactions