Question

Hydrogen bonds are formed in many compounds e.g., $H_{2}O,HFandN{H}_3$. The boiling point of such compounds depends to a large extent on the strength of the hydrogen bond and the number of hydrogen bonds. The correct decreasing order of the boiling points of the above compounds is :

• A. $HF>H_{2}O>N{H}_3$
• B. $H_{2}O>HF>N{H}_3$
• C. $N{H}_3>HF>H_{2}O$
• D. $N{H}_3>H_{2}O>HF$

Answer 1

The correct option is B $H_{2}O>HF>N{H}_3$

Strength of hydrogen bonding depends on the size and electronegativity of the atom.

Smaller the size of the atom, greater is the electronegativity and hence stronger is the $H-$bonding. Thus, the order of strength of H-bonding is $H...F>H...O>H...N$.

But each $HF$ molecule is linked only to two other $HF$ molecules while each $H_{2}O$ molecule is linked to four other $H_{2}O$ molecules through $H-$bonding.

Hence, the decreasing order of boiling points is $H_{2}O>HF>N{H}_3$.

Hence, the correct option is B.