Question

Why does the chlorine atom in hydrogen chloride acquire a slightly negative charge?

Answer 1

Because chlorine is an electronegative element......

Explanation:

And in the `H-Cl` molecule, chlorine polarizes electron density towards itself to give a `stackrel(+delta)H-stackrel(delta-)Cl` dipole. And in aqueous solution, the polarization goes to completion to give hydronium and chloride ions......

`stackrel(+delta)H-stackrel(delta-)Clstackrel(H_2O)rarrH_3O^+ + Cl^-`

What we write as `H_3O^+` is a conception only, and the actual acidium species is probably `H_7O_3^+` or similar.