Ochem questions!

[chiddler]

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Hello hello fellow....mellow....i can't think of anything else that rhymes.

I have a question that I serendipitously found on Y! Answers:

http://answers.yahoo.com/question/index?qid=20100103085428AA0jVvc

I understand the effect of electronegativity on hydrogen bonding. A more polar bond means stronger H bonds.

I do not understand the effect of atomic radius on hydrogen bonding, given equal electronegativities. So I don't understand the answer that the person responded with.

Thank yous.

 

[Pisiform]

I don't know if there is anything complex here, but my reasoning is that strongest bonds are formed with those that have high electronegativity and those that have high electronegativity are found to the top right and so have smaller radii. Don't know if that helps but yea its pretty much it.

 

[mmmmd]

More polar bonds means a stronger bond dipole moment.

So you want to have a larger distance between partial charges (the nucleus of the hydrogen and the valence shell of the other element). Bigger atomic radius --> bigger valence shell --> smaller distance between partial charges --> more polar --> strongest hydrogen bond.

 

[MedPR]

Hello hello fellow....mellow....i can't think of anything else that rhymes.

I have a question that I serendipitously found on Y! Answers:

http://answers.yahoo.com/question/index?qid=20100103085428AA0jVvc

I understand the effect of electronegativity on hydrogen bonding. A more polar bond means stronger H bonds.

I do not understand the effect of atomic radius on hydrogen bonding, given equal electronegativities. So I don't understand the answer that the person responded with.

Thank yous.

If you're talking about a bond between an atom and a Hydrogen, as opposed to a true hydrogen bond, then an atom with a larger radius (Iodine, for example) will form a weaker bond compared to an atom with a smaller radius but similar electron affinity, like Fluorine.

You can think of it like this: Iodine and Fluorine have the same number of valence electrons, but Iodine's electron cloud (atomic radius) is much larger than Fluorines, so those 7 valence electrons are much more spread out. H+ is basically looking for electrons to bond to. If an H+ encounters Iodine and Fluorine in solution, the H+ will have a much easier time finding a Fluorine elctron than an Iodine electron because Fluorine's valence electrons are more concentrated in a smaller area.

More polar bonds means a stronger bond dipole moment.

So you want to have a larger distance between partial charges (the nucleus of the hydrogen and the valence shell of the other element). Bigger atomic radius --> bigger valence shell --> smaller distance between partial charges --> more polar --> strongest hydrogen bond.

Only N O and F hydrogen bond, and they all have about the same atomic radius. Strongest hydrogen bond is based on polarity due to electronegativity.

Down a column = atomic radius, across a row = electronegativity.

 

[chiddler]

Ok I understand! Thanks!

I think I confused atomic radius with the length of bond.

 

[mmmmd]

Thanks, MedPR. I definitely made the opposite conclusion there on accident. Here's what I meant to say

More polar bonds means a stronger bond dipole moment.

So you want to have a larger distance between partial charges (the nucleus of the hydrogen and the valence shell of the other element). Smaller atomic radius --> smaller valence shell --> bigger distance between partial charges --> more polar --> strongest hydrogen bond.

I don't think that my newly updated explanation is wrong, but I do think you're explanation is spot on. Bigger radius = Lower valence shell density = less polar with a proton.

Gotta study for this exam, looks like.

 

[MedPR]

Thanks, MedPR. I definitely made the opposite conclusion there on accident. Here's what I meant to say



I don't think that my newly updated explanation is wrong, but I do think you're explanation is spot on. Bigger radius = Lower valence shell density = less polar with a proton.

Gotta study for this exam, looks like.

Well, technically N O and F have the same size valence shell (2p). The primary reason why oxygen hydrogen bonds (alcohol solution) are stronger than nitrogen hydrogen bonds (ammonia solution) is due to oxygen being more electronegative.