*Hydrogen Bonding

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Sara Sadrolsadat 1G
Posts: 39
Joined: Fri Sep 28, 2018 12:16 am

*Hydrogen Bonding

Postby Sara Sadrolsadat 1G » Sat Nov 24, 2018 6:24 pm

Do hydrogen bonds occur between H atoms and only O, F, or N atoms (since there are the most clearly electronegative)? Is a lone pair on the electronegative atom necessary for hydrogen bonding to occur? And if so, why? Can't there be an attraction between the hydrogen atom and the electronegative atom that is already bonded?

Andrea Zheng 1H
Posts: 61
Joined: Fri Sep 28, 2018 12:26 am

Re: *Hydrogen Bonding

Postby Andrea Zheng 1H » Sun Nov 25, 2018 12:14 pm

In lecture, we were told that it is present in molecules with N,O,or F.

We were also told that for a H bond to occur, there needs to be an H atom covalently bound to an electronegative atom and close to another electronegative atom that has an available lone pair. It needs a lone pair because the lone pair will form an interaction with the partial positive charge on the hydrogen atom. The partial positive charge is due to the unequal sharing between the H and the electronegative atom it is covalently bound to.

David S
Posts: 54
Joined: Fri Sep 28, 2018 12:15 am

Re: *Hydrogen Bonding

Postby David S » Sun Nov 25, 2018 12:38 pm

Yes, hydrogen bonds typically occur when a hydrogen is attached to a very electronegative atom
(N, O, F) because this results in a strong partial positive charge on the hydrogen. When a molecule containing this sort of H to N, O, F bond encounters another such molecule, a hydrogen bond will form if the N, O, or F in the other molecule has a lone pair.

Why? Since the Hydrogens in these situations have such strong partial positive charges, they are effectively like cations--their two shared electrons mostly hovering around the electronegative atom they are bonded to. This state of effective electron defficiency leads to the strong attraction of Hydrogen to the lone pair as if the hydrogen atom wants to form a coordinate covalent bond to take those two electrons and satisfy it's need for a duplet. If all the electrons on a neighboring electronegative atom are already stuck in bonds, there won't be any easily accessible electrons left for the hydrogen to be so strongly attracted to.

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