Determining H bonding

[Ice-cream]

I need help with determining whether hydrogen bonding with form between two substances. I know hydrgoen bonding occurs between H and F, N or O but does that mean whenever one molecule has a N and one has a H, then they can bond together by H bonding? Surely it can't be that easy!

[ed84c]

depends whether the N has all its electrons tied up with other with another atom. As far as I understand it if you have an electron gap, you can have another H atom.

[budullewraagh]

it all depends ont he compound's shape and structure really. if you give me some examples i can explain if there is hydrogen bonding present and how it affects the molecule

[Ice-cream]

ok for eg. HF and CH3CH2OCH2CH3...would those two form H bonding?

[budullewraagh]

nope

[budullewraagh]

hydrogen bonding tends to be more present in larger organic macromolecules like proteins and such

[Ice-cream]

but i thought HF is meant to have H bonding becuase H occurs with F, O and N right? what about S?

[budullewraagh]

HF is ionically bonded in the first place tho... one could say that hydrogen bonding occurs in aqueous HF, but it wouldnt occur between HF and diethyl ether

[jdurg]

Are you sure about HF being ionically bonded? I always thought that a compound that exists as a liquid or gas at room temperature was covalently bonded. I know that HCl is covalently bound, but easily ionizes in a water solution.

 

Okay. I did some further research and HF is definitely NOT ionic. It is a polar covalent bond, but assuredly not ionic. For a bond to be ionic, it generally must have an electronegativity difference of 2.0 or greater between the atoms. The difference between H and F is only 1.9 so it a strongly polar covalent bond.

[budullewraagh]

i was using linus pauling's definition and his electronegativities. according to pauling the electronegativity of fluorine is 3.98, and that of hydrogen is 2.20 which is a difference of 1.78. pauling said that a bond with an electronegativity difference greater than 1.7 is an ionic bond, thus making HF an ionic compound. of course, the terms "ionic bonding" and "electronegativity" are all subjective to one's opinion, so it's up to you