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Topic: Hydrogen bonds - Strong or weak?  (Read 19853 times)

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Offline neobenzene

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Hydrogen bonds - Strong or weak?
« on: August 12, 2012, 12:00:12 AM »
Hi! I have this major, basic doubt. Is intermolecular hydrogen bonding strong or weak? I have always been taught in school that they are "strong" bonds, but I came across this video on YouTube recently which states that they are "weak" bonds.

Which one is right?

Offline discodermolide

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Re: Hydrogen bonds - Strong or weak?
« Reply #1 on: August 12, 2012, 02:16:08 AM »
Hi! I have this major, basic doubt. Is intermolecular hydrogen bonding strong or weak? I have always been taught in school that they are "strong" bonds, but I came across this video on YouTube recently which states that they are "weak" bonds.

Which one is right?

A quote from a Wiki page:
"The hydrogen bond (5 to 30 kJ/mole) is stronger than a van der Waals interaction, but weaker than covalent or ionic bonds. This type of bond occurs in both inorganic molecules such as water and organic molecules like DNA."
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Offline neobenzene

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Re: Hydrogen bonds - Strong or weak?
« Reply #2 on: August 12, 2012, 02:23:58 AM »
But are hydrogen bonds strong enough to raise the melting/boiling points of a molecule?

Offline DrCMS

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Re: Hydrogen bonds - Strong or weak?
« Reply #3 on: August 12, 2012, 04:30:37 AM »
Yes and water is the classic example.

Offline neobenzene

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Re: Hydrogen bonds - Strong or weak?
« Reply #4 on: August 12, 2012, 04:49:33 AM »
So does that mean, NaI, which is very covalent according to Fajan's rule, has very high melting/boiling points? And by this, theoretically it should be more than that of water. Is that right?

Offline discodermolide

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Re: Hydrogen bonds - Strong or weak?
« Reply #5 on: August 12, 2012, 05:41:24 AM »
So does that mean, NaI, which is very covalent according to Fajan's rule, has very high melting/boiling points? And by this, theoretically it should be more than that of water. Is that right?

Yes it has a much much higher MPt. and BPt. than water, and not just theoretically.
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Offline neobenzene

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Re: Hydrogen bonds - Strong or weak?
« Reply #6 on: August 12, 2012, 09:43:27 AM »
Thank you very much, discodermolide and DrCMS!

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