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 CO32- 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 Compound Solubility in water MgSO4 Very soluble CaSO4 Sparingly soluble SrSO4 Insoluble BaSO4 When an ionic compound dissolved in water : MX(s) + aq  M+(aq) + X-(aq) Hsol < 0 This 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 < 0 Going 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.