Cl is an electronegative element and hydrogen is electropositive. Why are intermolecular interactions involving H and Cl not considered as H bonding? I read it in a book but there was no reason given for it.

  • $\begingroup$ H bonds have their bond energies in the order of ~10-20 kJ per mol. The bond energy of H-Cl is ~427 kJ per mol, which is too strong to be a H-bond $\endgroup$ – Aniruddha Deb Oct 26 '20 at 4:17
  • $\begingroup$ Why does H bonding depend on bond energy? $\endgroup$ – srijan Sri Oct 26 '20 at 4:21
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    $\begingroup$ A hydrogen bond by definition needs three centers to be formed: the donor atom(Dn), the hydrogen itself (H) and an acceptor atom (Ac) to form a setup like Dn–H···Ac .A bond between H and Cl has only two centres: the hydrogen(H) and chlorine(Cl). Without a third center to act as the donor or acceptor (depending on the convention you have followed) you can't have a "hydrogen bond" per se, it will just be a regular covalent or ionic bond $\endgroup$ – Yusuf Hasan Oct 26 '20 at 4:48
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    $\begingroup$ Yes, in each hydrogen bond of H2O, you can trace out three centres : O-H···O, where the O from one water molecule acts as the donor and also the first center, the hydrogen attached with donor oxygen forms the second center, while the oxygen from another water molecule as an acceptor and the third center $\endgroup$ – Yusuf Hasan Oct 26 '20 at 5:05
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    $\begingroup$ @orthocresol Maybe closing as unclear would be better idea... $\endgroup$ – Mithoron Oct 27 '20 at 13:59

As per my teacher, the reason we say that Chlorine does not form hydrogen bonds, even though its electronegativity is almost same as N (both have electronegativity values around 3.0 as per the Pauling Scale) is because :

Chlorine being a third period element, has a relatively larger size as compared with Nitrogen and Oxygen, so it has a quite large and more diffused electron cloud. Therefore the dipole-dipole interactions in HCl are not as strong as the ones encountered in HF and H₂O, and so it wouldnt be quite accurate for them to be called as Hydrogen Bonds, as the ones in HF and H₂O are much stronger.

Hope this answered your question.

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    $\begingroup$ This is not the inherent reason why the bonding between H and Cl is not considered hydrogen bonding, as on the Pauling scale , the electronegativity comes quite close to N, which is often involved in H bonds. The reason in this case has more to do with the definition of what we call a hydrogen bond, check my comments above for more details on the same. I believe that you have answered something else, while the OP has a misconception on a different aspect $\endgroup$ – Yusuf Hasan Oct 26 '20 at 8:32
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    $\begingroup$ As to why HCl might not show H-bonding in an extended network at low concentrations,yes, your reasoning could work as explained here in a related question. Although do note that clusters of HCl in a concentrated form may be obtained as shown here.As I said, I believe you have answered something else, and the OP was confused on a different point.Please modify accordingly $\endgroup$ – Yusuf Hasan Oct 26 '20 at 8:36
  • $\begingroup$ I do believe this was the actual question which the OP intended to ask...! I myself have had this doubt before. $\endgroup$ – SpaceSkiier Oct 26 '20 at 11:33
  • $\begingroup$ I think the question is ambiguous enough to admit both interpretations. I wouldn't downvote just based on that. But also, this question has been addressed elsewhere on SE. $\endgroup$ – orthocresol Oct 26 '20 at 14:19

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