Compounds of group 2 elements are less soluble in water than the corresponding salts of group 1 elements due to

Options

A. their higher ionisation enthalpy
B. their lower electronegativity
C. their lower hydration enthalpy
D. their higher lattice enthalpy.

Explanation

To answer the question regarding why compounds of group 2 elements are less soluble in water than the corresponding salts of group 1 elements, we can break down the explanation into several steps.

### Step-by-Step Solution:

1. **Identify the Groups**:
- Group 1 elements (alkali metals) include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs).
- Group 2 elements (alkaline earth metals) include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

2. **Charge of Ions**:
- Group 1 metals form cations with a +1 charge (e.g., Na⁺).
- Group 2 metals form cations with a +2 charge (e.g., Ca²⁺).

3. **Charge Density**:
- Charge density is defined as the charge of the ion divided by its volume. Group 2 cations have a higher charge (+2) compared to group 1 cations (+1), which results in a higher charge density for group 2 cations.

4. **Lattice Enthalpy**:
- Lattice enthalpy is the energy released when gaseous ions combine to form an ionic solid. Higher charge density leads to stronger electrostatic forces between the ions in the solid lattice.
- Group 2 compounds have higher lattice enthalpies compared to group 1 compounds due to the +2 charge of the cations.

5. **Solubility and Lattice Enthalpy Relationship**:
- There is an inverse relationship between lattice enthalpy and solubility: higher lattice enthalpy means lower solubility.
- Since group 2 compounds have higher lattice enthalpies, they are less soluble in water compared to group 1 compounds.

6. **Conclusion**:
- Therefore, the primary reason compounds of group 2 elements are less soluble in water than the corresponding salts of group 1 elements is due to their higher lattice enthalpy resulting from the higher charge density of the +2 cations.