Why Do Strongly Bonded Compounds Like HCl and NaCl Ionize in Water?

[krackers]

The bonds between H and Cl are strong, almost close to ionic, right? Thus if that is the case why does HCl readily ionize into H+ and Cl- upon contact with water? It doesn't make sense that such a strongly bonded compound should completely disassociate upon contact with water. Further, why does HF, another strongly bonded compound, not do the same thus making it a weak acid?

On a similar note, why does NaCl do the same? Na and Cl are very strongly ionically bonded, requiring lots of energy to break apart the bond. Yet on contact with water, they easily disassociate. Interactions between the Na, Cl, and the H2O dipole don't seem like they have enough energy to break it apart.

 

[Borek]

https://www.physicsforums.com/showthread.php?t=741566

 

[DrDu]

You should also take in mind that in the process of hydrolysis of an acid there is a new and very strong covalent bond being formed namely between H and O in $\mathrm{H_3O^+}$.

 

[abitslow]

HCl is covalent.

 

[LudusRex]

I can explain the ionization of HCl and NaCl in water through the concept of electronegativity and polarity. HCl is a polar covalent molecule, meaning that the shared electrons between hydrogen and chlorine are not evenly distributed. Chlorine is more electronegative than hydrogen, so it pulls the shared electrons closer to itself, creating a partial negative charge on the chlorine atom and a partial positive charge on the hydrogen atom. This uneven distribution of charge makes HCl a polar molecule.

When HCl comes into contact with water, the polar water molecules are attracted to the partial charges on the HCl molecule. This attraction can weaken the bond between hydrogen and chlorine, making it easier for the HCl molecule to break apart into H+ and Cl- ions. However, not all HCl molecules will ionize in water, as some may not come into contact with a water molecule or may not have enough energy to break apart.

In contrast, HF is a nonpolar covalent molecule, meaning that the shared electrons between hydrogen and fluorine are evenly distributed. This makes HF a weaker acid because the bond between hydrogen and fluorine is stronger and less likely to break apart in water.

Similarly, NaCl is an ionic compound, meaning that it is made up of positively charged sodium ions and negatively charged chloride ions held together by strong ionic bonds. When NaCl is added to water, the polar water molecules surround the ions and can weaken the ionic bonds, causing the compound to dissociate into its ions. However, the strength of the ionic bond between Na and Cl is still present and requires a significant amount of energy to completely break apart.

In summary, the strength of a bond between atoms does not solely determine the ability of a compound to ionize in water. The polarity and interactions between molecules also play a crucial role in the ionization process.