Why does HCl not exhibit Hydrogen bonding?

As the title says. Since Cl is more electronegative than N, why can't it form hydrogen bonds?

I'm assuming that the size of the Cl atom has something to do with it?

Reply 1

username920087

Yep, it's not a small enough atom. That's what we were told. :smile:

Reply 2

Another

Original post by ethery

Yep, it's not a small enough atom. That's what we were told. :smile:

But why does the size matter?

Chlorine, like Florine, has three pairs of lone electrons. The H-Cl bond also has a higher EN value than the N-H bond.

Surely that's all you need for a hydrogen bond?

Reply 3

FiniteMr

The lone pairs on a Cl- are very diffuse because Cl is larger than N, O, or F, so the force of attraction between the d+ Hydrogen in the HCl and a Cl in another molecule is not significantly more than normal VDW forces.

Reply 4

Mattywooda

I think it is because HCl is ionic. So it splits to H+ Cl-, not covalent which is a prerequisite for H bonds.

(edited 11 years ago)

Reply 5

username920087

Original post by Another

But why does the size matter?

Chlorine, like Florine, has three pairs of lone electrons. The H-Cl bond also has a higher EN value than the N-H bond.

Surely that's all you need for a hydrogen bond?

I've no idea, and I'm certain you don't need to know at the minute. I have had a look on chemguide though, and there's nothing mentioned there. I'll have a quick look through some of the resources I have.

Reply 6

username920087

Original post by Mattywooda

I think it is because HCl is ionic. So it splits to H+ Cl-, not covalent which is a prerequisite for H bonds.

But surely the atoms that do have hydrogen bonding should be ionic because of the electronegativity difference?

I feel like I'm trying to figure out a different problem altogether. :tongue:

Reply 7

Mattywooda

Nope, H bonding is only covalent, because they are partial charges. Ionic bonding is the "permanent" movement of electrons ie whole charges. H bonding is just a nice name for PD-PD bonds cause theyre extra strong. Ionic compounds don't have dipoles, they have charges...

Reply 8

Poopy

Something about it being a strong acid, and it dissociating completely in water, leaving you with only H+ and Cl- ions. Not sure

Reply 9

Onee-chan

Great question! The Chloride is electronegative enough to cause the hydrogen that it is attached to, to be d+ enough to form a hydrogen bond, so I guess had it not dissociated into H+ and Cl- ions in water, it should form H bonds (maybe it does when dissolved in ethanol?) but it's too big to actually form a hydrogen bond with a neighbouring d+ hydrogen.

Reply 10

Another

Original post by Mattywooda

I think it is because HCl is ionic. So it splits to H+ Cl-, not covalent which is a prerequisite for H bonds.

Oh for... seen this reasoning already, and a few reasons why it's wrong:

The HCl bond is polar covalent.

I'm assuming you're talking about HCl is solution. Yes, HCl does have ionic properties, and fully dissacociates in water. But the reason that HF doesn't fully dissacociate in solution is because of it's hydrogen bonds with water. Not the other way round.

HCl, on it's own, as a molecule however is a gas. And so is HF, and so is NH3.

Original post by Hypocrism

I think this is the answer I'm looking for... thanks very much xD

Original post by ethery

But surely the atoms that do have hydrogen bonding should be ionic because of the electronegativity difference?

I feel like I'm trying to figure out a different problem altogether. :tongue:

Actually... completely the opposite. Confusing, I know.

For a compound to dissolve, either

(1) the water must be able to overcome the intermolecular forces between the molecule, or
(2) the water must be able to split the compound into ions.

Before I go on, both HF and HCl are covalent bonds. No metal is involved, so no ionic bonding here. But to get them into ionic states (like, H+ and Cl-) the water must be able to overcome their intramolecular bond enthalpies.

For HCl, this is fine. Hydration energy is higher than bond enthalpy, so it dissacociates fine. But HF contains hydrogen bonds - so the water must first have the energy to break these strong hydrogen bonds (remember, F has three lone pairs) and then have the energy to break the intramolecular bonds. The hydration energy actually isn't high enough to complete this alot of the time, which is why HF only forms a weak acid in solution.

(edited 11 years ago)

Reply 11

Mattywooda

Original post by Another

For HCl, this is fine. Hydration energy is higher than bond enthalpy, so it dissacociates fine. But HF contains hydrogen bonds - so the water must first have the energy to break these strong hydrogen bonds (remember, F has three lone pairs) and then have the energy to break the intramolecular bonds. The hydration energy actually isn't high enough to complete this alot of the time, which is why HF only forms a weak acid in solution.

Fair enough, I just googled it :L Also you're forgetting the attractive force the ions have on the water molecules affecting its entropy. F- is much stronger than Cl- so would decrease entropy much more than Cl- another reason why it doesn't dissociate.

Reply 12

SomePotential

Someone else asked the same question in another thread:

Original post by SomePotential

I wondered that my self. Chlorine is a larger atom, so the attraction between the partial charges won't be as large even though Chlorine has a higher electronegativity. This is because the electron pairs in Chlorine are too diffuse (spread out), and so only form a strong permanent dipole-dipole. Scientists have created/witnessed hydrogen bonding in HCl, but I think we can ignore that.

Edit: I had a look at this again in more depth and, while for CHEM1 we only need to know about Hydrogen bonds between N, O and F atoms, hydrogen bonding can exist between other molecules.
"A hydrogen bond is an attractive interaction between two species that arises from a link of the form A-H···B, where A and B are highly electronegative elements and B possesses a lone pair of electrons. Hydrogen bonding is conventionally regarded as being limited to N, O, and F but, if B is an anionic species (such as Cl^-), it may also participate in hydrogen bonding. There is no strict cutoff for an ability to participate in hydrogen bonding, but N, O, and F participate most effectively."^[1]

So Hydrogen bonding isn't black and white. It's also possible that the Pauling scale isn't correct when compared with experimental data, and it was made by Pauling using algorithms so might not be 100% accurate. Also, Eric Jacobsen at Harvard as developed catalysts which use Hydrogen Bonding in HCl. ^[2] So it's actually more interesting that what we learn in CHEM1, but for the exam we just need to focus on Nitrogen, Oxygen and Fluorine.

1. www.as.utexas.edu/astronomy/education/spring07/scalo/secure/AtkinsNoncovalent.pdf
2. http://www.quora.com/Chemistry-physical-science/Why-cant-HCl-hydrogen-bond

Reply 13

Dhanushkadsilva

Nitrogen is more electronegative than Chlorine. When N forms NCl3, the oxidation state of N is -3 and oxidation state of Cl is 1. That happens because N can pull electrons in N-Cl bond. That means N is more electronegative

Reply 14

Anonymouspsych

Original post by Dhanushkadsilva

This is a thread from 6 years ago.... lmao. Nice try though

Reply 15

username3249896

Original post by Dhanushkadsilva

oxidation state of N in NCl3 is +3 and oxidation state of Cl is -1.

Cl is more electronegative than N.
Cl has electronegativity 3.16 on the Pauling scale while N has electronegativity 3.04

Reply 16

Dhanushkadsilva

Original post by BobbJo

oxidation state of N in NCl3 is +3 and oxidation state of Cl is -1.

Cl is more electronegative than N.
Cl has electronegativity 3.16 on the Pauling scale while N has electronegativity 3.04

When NCl3 reacts with water, it doesn't undergo any redox reaction. Only a hydrolysis will occur. There NCl3 reacts with water to result NH3 and HOCl in which the oxidation states are N = -3 and Cl= +1 respectively. But when PCl3 reacts with water it results not HOCl but HCl since the oxidation number of Cl in PCl3 is -1

Reply 17

charco

Study Forum Helper

Original post by BobbJo

oxidation state of N in NCl3 is +3 and oxidation state of Cl is -1.

Cl is more electronegative than N.
Cl has electronegativity 3.16 on the Pauling scale while N has electronegativity 3.04

Don't forget that electronegativity and oxidation numbers are artificial constructs - just tools to assist in the explanation of empirical observation.

There are several different electronegatively scales constructed from functions based on ionisation energy and electron affinity (and other quantitative measurements).

Empirical observation suggests that nitrogen is more electronegative than chlorine, regardless of the EN values selected.

NH₃ (Mr 17) b.p. = -33.3 ºC
HCl (Mr 36.5) b.p. = -85.1 ºC

Clearly the London Dispersion forces in HCl are greater than in ammonia, but the boiling point demonstrates that the intermolecular forces are much greater in ammonia.

The only conclusion is that nitrogen is more electronegative than chlorine.