Why do acids ionize in solution if they are covalently bonded?

Maybe I am wrong, but I thought acids were covalently bonded since hydrogen doesn't form ionic compounds. For example, wouldn't $\ce{HCl}$ look like:


![structure of HCl](https://i.stack.imgur.com/evtWN.png) 


Since the electrons are shared, why does it break into $\ce{H+}$ and $\ce{Cl-}$ in solution?




![enter image description here](https://i.stack.imgur.com/kpcXu.jpg)


Because it is energetically favourable ($\Delta{G}<0$) for hydrogen chloride to react with water to form hydronium( $\ce{ H3O+}$) and chloride ions.


Remember that $\ce{ H+}$ does not exist as $\ce{ H+}$ in water, but rather as $\ce{ H3O+}$.


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Your are right. But you have to remember that the bond between hydrogen and chlorine (for example) is covalent polar one. When you introduce this molecule into water which is a polar solvent with a dipole moment of 1.85 D, the polarization of the molecule $\ce{HCl}$ increases. We have then two solvated ions $\ce{H\_3O^+}$ and and $\ce{Cl^-}$. And as water has also a high dielectric constant $\epsilon\_r=80$, the electrostatic force between $\ce{H\_3O^+}$ and $\ce{Cl^-}$ will decrease by a factor of 80. So, the the bond between $\ce{H\_3O^+}$ and $\ce{Cl^-}$ will weaken and we have ionization of the acid.


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