Is HCl ionic or molecular?

In summary, HCl is a stable molecule with partial ionic character in the gas phase, but it dissociates into neutral atoms at higher bond distances. In aqueous solution, it forms ions due to the low energy pathway of ionic bonding. Most Bronsted-Lowry acids exhibit similar behavior, with differing properties in the gas and solution phases due to the enthalpy of solvation of ions.
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I have thought the HCl is an ionic compound since it disassociates in water. However I read in my chemistry book that HCl is molecular. So what is it? Are all acids molecular or just the ones like HF, HCl, HBr, etc?
 
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In solution, they're dissociated to whatever degree. As solids, you're looking at a very small cation which can polarize charge on the anions and lead to that "gray" area between ionic and covalent bonds.
 
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barryj said:
I have thought the HCl is an ionic compound since it disassociates in water. However I read in my chemistry book that HCl is molecular. So what is it? Are all acids molecular or just the ones like HF, HCl, HBr, etc?
HCl is a stable molecule that can exist in the gas phase. As an isolated molecule, it has a permanent dipole moment, so the sharing of electrons in this molecule is not equal -- chemists would say that it shows partial ionic character. Interestingly, as you increase the bond distance of the molecule in the gas phase, it will dissociate into neutral hydrogen and neutral chlorine atoms (lowest energy path) -- i.e. the percent ionic character will decrease with increasing bond length. You can see the same behavior in a gas-phase NaCl molecule, as well. The diatomic molecule shows partial ionic character, but will dissociate to neutral atoms. You can read about some interesting chemical physics about the reverse process if you look up "harpoon mechanism".

If you increase the bond distance in aqueous solution, you will get ions (H+ and Cl-). The reason for this difference is that the ionic pathway is lower energy in solution because the enthalpy of solvation of the ions is very exothermic.

Most Bronsted-Lowry acids would behave the same way. I.e. differing gas-phase and solution-phase behavior, due to the large negative enthalpy of solvation of the ions.
 

1. What is the chemical formula for HCl?

The chemical formula for HCl is written as HCl because it is composed of one hydrogen atom and one chlorine atom.

2. Is HCl an ionic or molecular compound?

HCl is a molecular compound because it is composed of covalently bonded atoms, rather than ions.

3. How is HCl formed?

HCl is formed through the chemical reaction of hydrogen gas (H2) and chlorine gas (Cl2).

4. What is the difference between ionic and molecular compounds?

Ionic compounds are formed through the transfer of electrons, resulting in ions with opposite charges that are held together by electrostatic forces. Molecular compounds, on the other hand, are formed through the sharing of electrons between atoms in a covalent bond.

5. Is HCl a strong or weak acid?

HCl is a strong acid because it dissociates completely in water, producing a high concentration of hydrogen ions (H+) in solution.

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