Question

Select the correct statements.

• A. The heat of hydration of the dipositive alkaline earth metals ions increases with increase in their ionic size.
• B. Hydration of alkali metal ions is less than that of alkaline earth metals.
• C. Alkaline earth metal ions, because of their much larger charge to size ratio, exert a much stronger electrostatic attraction on the oxygen of water molecule surrounding them.
• D. The melting point of sodium halides follow the order $NaF>NaCl>NaBr>NaI$.

Answer 1

Answer: (B), (C), (D)

The melting point of sodium halides follow the order $NaF>NaCl>NaBr>NaI$.

a) Down the group, due to the increase in ionic size, the hydration energy of a dipositive ion decreases.

b) The size of the alkaline earth metals is smaller than that of the corresponding alkali metals. So, their hydration energy is lower than that of the alkaline earth metals.

c) Alkaline earth metal ions, because of their much larger charge to size ratio, exert a much stronger electrostatic attraction on the oxygen of water molecule surrounding them.

d) Ionic radius decreases in the order $I^{-}>B{r}^{-}>C{l}^{-}>F^{-}$. According to fajan's rule, covalent character decreases as $NaI>NaBr>NaCl>NaF$. So, $NaF$ is the most ionic and hence it has the highest melting point. The melting point order is $NaF>NaCl>NaBr>NaI$