Chapter 18, Problem 17TE

Why is a water molecule more attracted to a calcium ion than a sodium ion?

To determine

Reason behind more attraction between water molecule and calcium ion than between the water molecule and sodium ion.

Answer to Problem 17TE

The water molecule is more attracted to a calcium ion as it has $+2$ charge and a bigger size than that of sodium ion.

Explanation of Solution

A water molecule is a polar molecule having an oxygen atom as a central atom. Since the oxygen atom contains six electrons in its existing outermost shell and thus there are two nonbonding pairs of electrons present.

These nonbonding electron pairs can attract the positively charged ions. They have a tendency to attract sodium ion as well as calcium ion. The sodium ion has a $+1$ charge and the calcium ion has a $+2$ charge. The size of sodium is small as compared to the calcium ion as they are present in different periods.

Thus, due to the smaller size of sodium ion and a lesser $+1$ charge has a less tendency to attract the water molecule then the calcium ion which has a bigger size and a higher $+2$ charge has more tendency to attract water molecules.

Conclusion:

Therefore, the water molecule is more attracted to a calcium ion as it has $+2$ charge and a bigger size than that of sodium ion.