# Why does NH3 have stronger intermolecular forces of attraction than Cl2?

May 15, 2018

$\text{...because of hydrogen bonding....}$

#### Explanation:

Hydrogen bonding occurs for molecules in which hydrogen is bound to a STRONGLY electronegative atom such as fluorine, oxygen, or nitrogen. And so it occurs primarily in the element hydrides....$N {H}_{3}$, $H F$, ${H}_{2} O$... Now hydrogen-bonding acts as an intermolecular force that STRONGLY ELEVATES the boiling point...i.e. $\stackrel{\delta +}{H} - \stackrel{{\delta}^{-}}{F} \cdots \stackrel{\delta +}{H} - \stackrel{{\delta}^{-}}{F} \cdots H - \stackrel{{\delta}^{-}}{F} \cdots H - F \cdots$..

And if we look at the normal boiling points...

$\text{ammonia}$ $- 44$ ""^@C

$\text{hydrogen fluoride}$ $+ 19$ ""^@C

$\text{water}$ $+ 100$ ""^@C

...all of these are high for such SMALL molecules. The boiling point of water is ASTONISHINGLY high...and this is to be attributed to the effectiveness and extent of hydrogen-bonding....

On the other hand, for $C {l}_{2}$, while this is a bigger molecule, with more electrons to contribute to the dispersion force, dichlorine is NON-POLAR with NO dipole interaction to contribute to the intermolecular force, and hence a reduced normal boiling point of $- 33.8$ ""^@C...