Question

The hydrides of the first elements in groups 15 - 17, namely $N{H}_3,H_{2}O$ and $HF$ respectively, show abnormally high values for melting and boiling points. This is due to:

• A. small size of $N,O$ and $F$
• B. the ability to form extensive intermolecular $H$-bonding
• C. the ability to form extensive intramolecular $H$-bonding
• D. effective van der Waal's interaction

Answer 1

Answer: (B)

the ability to form extensive intermolecular $H$-bonding

The hydrides of the first elements in groups 15 - 17, namely $N{H}_3$, $H_{2}O$ and HF respectively, show abnormally high values for melting and boiling points. This is due to the ability to form extensive inter-molecular H-bonding. In these hydrides, H atom is attached to highly electronegative N, O or F atoms resulting in stronger hydrogen bonds which lead to molecular associations. Large amount of energy is needed to break these hydrogen bonds.