Question

$Be{{F}_{2}}$ Is soluble in water, whereas the fluorides of other alkaline earth metals are insoluble because of
A) Greater hydration energy of $B{{e}^{2+}}$ ion as compared to crystal lattice
B) Covalent nature of $Be{{F}_{2}}$
C) Ionic nature of $Be{{F}_{2}}$
D) None of these

Answer 1

Hint: Consider the size of the cations in the alkaline earth metals and the factors that alter the solubility should be considered.

Complete step by step answer:
-The requirement of the question is the reason for the solubility of $Be{{F}_{2}}$ in water.
-The factor that affects or has an effect on solubility is of hydration energy.
Hydration enthalpy of hydration energy can be defined as the amount of energy which is released during the hydration of one mole of salt in the solvent.
Here water is taken as the solvent.
-Greater is the value for hydration energy, greater will be the solubility of the salt in the solvent,
So we can summaries this idea as,
Solubility is directly proportional to the hydration energy,
Solubility $\alpha $ hydration enthalpy
Next we have to consider the factors that affect the hydration energy.
Here $Be{F}_{2}$ the cation $B{{e}^{2+}}$, belongs to the second group in the periodic table which is called alkaline-earth metal.
While moving down the group the hydration energy decreases, so as the size increases the hydration enthalpy decreases.
Be is the first element in the second group with least size, so it possesses the highest hydration enthalpy and hence is soluble in water, whereas others are insoluble.
If we look at the options, option (A) supports the question.
For option (B), covalent compounds are formed by Be due to the highest ionization potential while other elements form the ionic compounds only, but the covalent nature does not supports the solubility of $Be{{F}_{2}}$
Option (C) is invalid since all the other elements in the ${{2}^{nd}}$ group form ionic bonds.

By comparing the options we can say that the correct answer for the question is option (A).

Note: The size parameter of the cations and anions should be importance for such type of questions,
The magnitude of hydration energy mainly depends on the density of the charge, more the charge with smaller size cation will have greater hydration enthalpy.