GROUP II

Thermal stability of Group II carbonates and nitrates.

MgCO3 , Mg(NO3)2

CaCO3 , Ca(NO3)2

SrCO3 , Sr(NO3)2

BaCO3 , Ba(NO3)2

- Thermal stability increase, more difficult to decompose.- Ionic radius increase, - charge density decrease, - more difficult to distort the large CO3

2- and NO3- anion.

- Compound more difficult to decompose.

In decomposition, the large CO32- and NO3

- anions are first distorted decompose into smaller O2- anion.

This distortion produced by metal cation (M2+) which forms a stronger bond with the small O2- ion produce the more stable Group II oxide.

Solubility of Group II sulphates and oxides

When an ionic compound dissolved in water :MX(s) + aq M+(aq) + X-(aq)Hsol < 0This process involves 2 imaginary stages:

1) MX(s) M+(g) + X-(g), -Hlatt > 0

2) M+(g) + X-(g) + aq M+(aq) + X-(aq), Hhyd < 0Going down the group, ionic radius increase, lattice energy

decrease (less exothermic)Hence step 1 becomes less endothermic and step 2 becomes

less exothermic.Change of Hhyd is more compare to lattice energy.Going down the group, Hhyd decrease more compare to

lattice energy.

Solubility in water decrease.

Compound Solubility in water

MgSO4 Very soluble

CaSO4 Sparingly soluble

SrSO4 Insoluble

BaSO4 Insoluble