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

1 Answer
May 15, 2018

Answer:

#"...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#...