I was doing an acid-catalyzed mechanism and I ran into hydronium ($\ce{H3O}$) and I wasn't able to figure out why its structure is the way it is. If you look at the structure, you see the hydrogens, and an oxygen; however, the oxygen has two electrons remaining outside of it. This is confusing to me as If you add up all the electrons (3 from Hydrogens, 2 from the remaining oxygen), we have a total of 5 valence electrons, even though we should have a total of six. I would assume that each hydrogen would take up one electron from the oxygen each, thus three electrons would remain on the oxygen.
Could someone please explain why this is? Thanks.
Here is a little sketch I made to show what I mean: