# Bonding in protonated molecule

We have $\ce{H2O}$ with two lone pairs on the oxygen atom and $\ce{H3O+}$ with only one lone pair on the oxygen atom.

One electron from the four non-bonding electrons has made a bond with the third hydrogen atom, so we should still have three electrons left. Why do we have only two?

• What is the charge of $\ce{H3O+}$... – bon Oct 10 '17 at 11:00

The answer is quite simple: When you have $\ce{H2O}$, it means you have two hydrogen and one oxygen atoms. Each hydrogen brings 1 electron, while the oxygen brings 6.
The solution to your question is, that you do not have $\ce{H3O}$, but $\ce{H3O+}$! The plus means, there is one electron less in the molecule, because you don't bring another H (with one electron) into the molecule, but rather just a proton ($\ce{H+}$ with the electron removed).
• Well, it only formally is a proton. Actually, there are no protons in aqueous solutions. $\ce{H+}$ is usually just short for $\ce{H3O+}$. But that is not important to answer the question. It is important, however, to count the available electrons and deduct 1 for the positive charge! – basseur Oct 10 '17 at 17:23