Group 2 Elements

• Elements in Group 1 and Group 2 are known as: s-block elements because their valence [bonding] electrons are in the s orbitals.

M  → M2+

+

2e-

• These elements give away 2 electrons when they react.
• As the Group 2 elements cause the reduction of other compounds or elements (as it gives two electrons to another compound), we say it is a good Reducing agent.
• Reactivity increases as you go down the Group.  This means they lose their electrons more readily.
• This means as you go down Group 2, they become better Reducing agents.

Physical Properties

• High melting and boiling points
• Low density metals
• Form colourless compounds/white when solid

Atomic Radius

The atomic radius increases as you go down the group due to:

• The increased number of electron shells
• The less effective nuclear attraction

1st Ionisation energy

The first ionisation energy decreases as you go down the group due to:

• despite the increased nuclear charge
• there is increased electron shielding
• the atomic radii increases
• Overall the effective nuclear attraction decreases.
• Become more reactive as you go down group 2.

Group 2 elements reacted with oxygen

• Group 2 metals react vigorously with oxygen to form simple ionic oxide

e.g. 2Mg (s) + O₂ (g) → MgO (s)

• It reacts with increasing vigour as you go down the group

Group 2 elements reacted with water

• Beryllium does not react with water
• The rest of the group 2 metals react with increasing vigour as you go down the group to form a metal hydroxide, M(OH)₂ and hydrogen gas

e.g. M (s) + 2H₂O (l) → M(OH)₂ (aq) + H₂ (g)

• These hydroxides have increasing solubility in water to form alkaline solutions.

Group 2 oxides and hydroxides
 

• Group 2 oxides and hydroxides are bases
• They are neutralised by acids to from a salt and water

e.g. MgO (s) + 2HCl (aq) → MgCl₂ (aq) + H₂O (l)
       Ca(OH)₂ (s) + 2HCl → CaCl₂ (aq) + H₂O (l)
 
Oxides

• Group 2 oxides react with water to form a solution of the metal hydroxide.
• These solutions usually have a pH of 10-12

e.g. MgO (s) + H₂O (l) → Mg(OH)₂ (aq)
 
Hydroxides

• Group 2 hydroxides dissolve in water to form alkaline solutions.

e.g. Ca(OH)₂ (s) + aq → Ca²⁺ (aq) + 2OH^- (aq)

• The solubility of the hydroxides in water increases as you go down the group.

Uses of group 2 hydroxides?
 
- Calcium hydroxide, Ca(OH)₂ is used by farmers and gardeners to neutralise acidic soils
- Magnesium hydroxide, Mg(OH)₂ is used in 'Milk of magnesia' to relieve indigestion. It works by neutralising any excess acid in the stomach.
 
Group 2 Metal Carbonates
 
THERMAL DECOMPOSITION is the breaking of a chemical substance using heat into at least 2 smaller substances.

• The group 2 carbonates undergo thermal decomposition to form the metal oxide and carbon dioxide gas.

 e.g. MgCO₃ (s) → MgO (s) + CO₂ (g)

• The group 2 carbonates decompose at a higher temperatures as you go down the group.

• e.g. BaCO₃ needs the most energy to break the bonds in the compound.

 

 

Calcium Compounds

 

 



 
 
- Most calcium is found as calcium carbonate in limestone
 
Uses of calcium compounds

• Limestone - Calcium carbonate CaCO₃ (s) - making cement
• Quicklime Calcium Oxide CaO (s) - iron purification
• Slaked Lime - Solid calcium hydroxide Ca(OH)₂ (s) - Soil Treatment
• Lime water - Aqueous calcium hydroxide Ca(OH)₂ (aq) - testing for CO₂