Drawing the Lewis Structure for H3O+

Viewing Notes:

  • H3O+ is also known as the Hydronium Ion and is very important in acid-base chemistry.
  • Hydrogen atoms only need 2 valence electrons to have a full outer shell.

Transcript: Hi, this is Dr. B. Let's do the Lewis structure for H3O+, the hydronium ion. On the periodic table, Hydrogen's in group 1, 1 valence electron; but we have 3 Hydrogens. Plus Oxygen, group 6 or 16; 6 valence electrons. And this plus sign means we've lost a valence electron, we've lost a negative charge. So we actually need to subtract 1. That gives us 3 + 6 is 9, minus 1: 8 valence electrons. Let's put the Oxygen at the center. Hydrogens always go on the outside right like that. Let's put some valence electrons around the atoms. Start by forming chemical bonds: 2, 4, 6. We have 2 more. Let's put them up here on the Oxygen, 8.

So Hydrogen only needs 2 to have a full outer shell so the Hydrogens are all good. Oxygen needs 8, it has 8, and we've used up all of the valence electrons. We'll finish by putting brackets around it, like this here, to show that it's an ion, and put a plus charge up here so everyone knows that it's a positive ion, a cation.

That's the Lewis structure for H3O+, the hydronium ion. This is Dr. B., and thanks for watching.