Question

The hydrides of the first elements in groups $15 - 17$, namely $NH_3, H_2O$ 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 intramolecular H-bonding
• C. the ability to form less intramolecular H-bonding
• D. effective van der Walls interaction

Answer 1

Answer: (B)

the ability to form extensive intramolecular H-bonding

Answer 2

Hydrides of $N , O$ and $F$ because of the small size and high electronegativity of elements, have ability to form extensive intermolecular (i.e., between two molecules) hydrogen bonding. Thus, a large amount of energy is required to break these bonds, i.e., the melting and boiling points of hydrides of these elements are abnormally high.