Are These Intermolecular Interactions Hydrogen Bond?

We have 2 criteria for the interaction between 2 molecules to be considered hydrogen bond.

1. Hydrogen is bonded to electronegative fluorine, oxygen or nitrogen
2. Electronegative fluorine, oxygen or nitrogen is partial negative charge

230515 criteria for h bond

Some students might find criteria 2 redundant, since F/O/N must be partial negative charge if it is bonded to hydrogen as mentioned in criteria 1.

This is true for interaction between pure species such as HF to HF, H2O to H2O or NH3 to NH3.

However in a mixture when 2 different species interact with each other, we can appreciate criteria 2 better.

Let's consider the following 5 examples.

A. CH4 and H2O

230515 a ch4 and h2o

Criteria 1 is not met since hydrogen is bonded to non-electronegative carbon. C-H bond is considered non-polar.

Criteria 2 is met since oxygen is bonded to hydrogen hence oxygen is partial negative.

Therefore this interaction is not hydrogen bond.

B. HF and NH3

230515 b hf and nh3

Criteria 1 is met since H is bonded to F.

Criteria 2 is met since N is bonded to H hence N is partial negative.

This interaction is hydrogen bond.

C. H2O and COH2

230515 c h2o and coh2

Criteria 1 is met since H is bonded to O.

Criteria 2 is met since O is bonded to less electronegative C hence O is partial negative.

Notice it's not a requirement for O to be bonded to H, it just needs to be bonded to a less electronegative element in order to be partial negative.

Hence this interaction is hydrogen bond.

D. NH3 and N2

230515 d nh3 and n2

Criteria 1 is met since H is bonded to N.

Criteria 2 is not met since N is bonded to same element hence the N-N triple bond is nonpolar.

N in N2 will not attract H in NH3.

Therefore this interaction is not hydrogen bond.

E. H2O and OF2

230515 e h2o and of2

Criteria 1 is met since H is bonded to O.

Criteria 2 is not met since oxygen is bonded to more electronegative F hence O is partial positive and will not attract H in H2O.

Therefore this interaction is not hydrogen bond.

Topic: Intermolecular forces, Physical Chemistry, A Level Chemistry, Singapore

Back to other previous Physical Chemistry Video Lessons.

Found this A Level Chemistry video useful?

Please LIKE this video and SHARE it with your friends!

Join my 10,000+ subscribers on my YouTube Channel for new A Level Chemistry video lessons every week.

Check out other A Level Chemistry Video Lessons here!

Need an experienced tutor to make Chemistry simpler for you?

Do consider signing up for my JC Chemistry Tuition classes at Bishan or on-demand video lessons!