Question

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

Answer 1

`"...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....`NH_3`, `HF`, `H_2O`... Now hydrogen-bonding acts as an intermolecular force that STRONGLY ELEVATES the boiling point...i.e. `stackrel(delta+)H-stackrel(delta^-)Fcdotsstackrel(delta+)H-stackrel(delta^-)FcdotsH-stackrel(delta^-)FcdotsH-Fcdots`..

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

`"ammonia"` `-44` `""^@C`

`"hydrogen fluoride"` `+19` `""^@C`

`"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 `Cl_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`...