Polar Covalent Bond in HCl question

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Discussion Overview

The discussion revolves around the nature of the polar covalent bond in hydrochloric acid (HCl) and its implications for molecular interactions, including potential hydrogen bonding and ion attraction. Participants explore the characteristics of HCl as a polar molecule, comparing it to other compounds like HF and discussing its behavior in the presence of ions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the polar covalent bond in HCl leads to a polar molecule due to its asymmetry, suggesting that the partially positive hydrogen could attract the partially negative chlorine of another HCl molecule.
  • Others argue that while there may be some attraction between HCl molecules, it is unlikely to form a chain due to the relatively weak interactions compared to stronger hydrogen bonds seen in other molecules like HF.
  • A participant mentions that HCl can attract negative ions due to the partially positive hydrogen and that the partially negative chlorine can attract positive ions from other compounds, although they specify that KCl may not be a suitable example due to the closed electron shell of K+.
  • Another participant compares the boiling points and molecular behavior of HCl and HF, noting that HCl does not exhibit significant hydrogen bonding and primarily exists as lone molecules in vapor form.

Areas of Agreement / Disagreement

Participants express differing views on the extent of molecular interactions in HCl, particularly regarding the formation of chains and hydrogen bonding. There is no consensus on the strength or significance of these interactions.

Contextual Notes

Participants reference the differences in molecular size and electronegativity between hydrogen, chlorine, and fluorine, which may influence the nature of interactions. The discussion also touches on the limitations of using KCl as an example for ion attraction due to specific electronic configurations.

Who May Find This Useful

This discussion may be of interest to those studying chemistry, particularly in understanding molecular interactions, polar covalent bonds, and acid-base behavior.

ProjectFringe
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If my understanding is correct, the polar covalent bond in HCl creates a polar molecule because the molecule is unsymmetrical.

1. Does this mean that the partially positive H of one HCl molecule will be attracted to the partially negative Cl of another HCl molecule and vice versa, to create a chain of HCl? If so, what is this called?

2. In regards to an HCl molecule, does this also mean that the partially positive H can attract negative ions and the partially negative Cl can attract positive ions from another compound such as KCl?
 
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1. I'm assuming you are talking about hydrogen bonding-like behavior. In that sense, it sort of happens but the attraction is much much smaller than e.g. oxygen and nitrogen. This is because although chlorine have high electronegativity, due to its atom size, the electron density is not high enough for hydrogen bonding. As such, it's improbable that it creates a chain of HCl.

2. Due to the reason above, I don't think you can observe a hydrogen bond-like behavior or significant attraction for chlorine atom in HCl. The dipole attraction do happen to some extent though, and this affects the boiling point. As for hydrogen bond for the hydrogen in HCl, hydrogen bond between fluorine of HF and hydrogen of HCl has been documented before (HF-HCl complex).
https://aip.scitation.org/doi/abs/10.1063/1.434691
 
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Got it! Thanks:biggrin:
 
ProjectFringe said:
If my understanding is correct, the polar covalent bond in HCl creates a polar molecule because the molecule is unsymmetrical.

1. Does this mean that the partially positive H of one HCl molecule will be attracted to the partially negative Cl of another HCl molecule and vice versa, to create a chain of HCl? If so, what is this called?
It probably does not happen, but if it does, it would be called "associate".
Compare HF. HF has molar mass of 20. It boils at +19 Celsius. And even above the boiling point, the molar mass of vapour is much bigger than 20, non-integer and varies strongly with temperature and pressure - at room temperature it is around 50 or so. The reason is that the vapour has equilibrium of various hydrogen bonded associates - (HF)2, (HF)3, some HF and so on, which equilibrium easily shifts.
In contrast, HCl boils at -85, and the vapour seems to be mostly lone molecules.
The reason is that H is much smaller than Cl. With the smaller F, H can give both polar covalent bond and hydrogen bond. With Cl, the polar covalent bond is weaker, and hydrogen bond cannot be formed.
ProjectFringe said:
2. In regards to an HCl molecule, does this also mean that the partially positive H can attract negative ions and the partially negative Cl can attract positive ions from another compound such as KCl?
It can attract negative ions - which is why HCl is a strong acid and reacts with a lot of salts. Like
HCl+F-=HF+Cl-
Partially negative Cl can attract positive ions from another compound. Actually not KCl, specifically, because K+ has a closed electron shell. On the other hand, partially negative Cl readily attracts positive ions from compounds like AlCl3.
 
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