Which molecule shows the least hydrogen bonding, CH4, HF, H2O, or NH3?

Or which would tou expect to show the least, and why?
 
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1,426 IKU
Posted on May. 3rd, 2008

Hydrogen bonding is exhibited between a polar molecule containing hydrogens with another molecule with an electronegative polar functional group that has available lone-pair electrons. A good example of this would be water. Water is a polar molecule since it is asymmetrical and has a negative and positive end. The hydrogen bonding occurs between the oxygen of one molecule with the hydrogen of another. This accounts for surface tension on water.

Now, to answer your question, Water has stronger hydrogen bonding, but not stronger hydrogen bonds than HF, but it does have stronger hydrogen bonds than ammonia.

There are two things that affect the intermolecular forces in these molecules: the strength of the H-bond itself, and the number of them that can be formed between neighboring molecules.

The larger the difference in electronegativity of the H atom and the other atom (N, O, and F), the stronger the H-bond. Therefore the order is N < O < F.

However, HF can only form one H-bond to one neighbor, while water can form two thus promoting more intermolecular interactions. Ammonia, while it has 3 N-H bonds, has far weaker H-bonds due to the lower electron density on the N-atom compared to the O-atom in water.

Lastly, I would like to add that CH4 (methane) is not polar so it is not able to form hydrogen bonds with other molecules.

Thanks for the question!

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1,416 IKU
Posted on May. 3rd, 2008

Well from what you show, HF shows the least hydrogen bonding. This is how I break it down (if i am wrong, somebody please correct me) but look at it. CH4 shows you that there are four hydrogens to the carbon molecule. Then with H20 there are two hydrogen to the oxygen molecule. With NH3 there are three hydrogens to the nitrogen molecule. What HF shows is that there is only one bond between the hydrogen and then Flourine molecule hence the least hydrogen bonding.

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