Hydronium (H3O+) Ion Lewis Structure

Hydronium ion contains hydrogen and oxygen atoms. Lewis structure of hydronium ion (H3O+) contains three O-H bonds. There is +1 charge and one lone pair on oxygen atom in H3O+ lewis structure.

H3O+ lewis structure

H3O+ hydronium ion lewis structure

Each hydrogen atom has linked with oxygen atom. Only one lone pair exist on oxygen atom. Therefore, there is a +1 charge on oxygen atom in the lewis structure of H3O+ ion.

Steps of drawing lewis structure of H3O+

When we draw a lewis structure, there are several guidelines to follow. Number of steps can be changed according the complexity of the molecule or ion. Because H3O+ is an ion, we will have more steps than drawing a simple molecule. However those all steps are mentioned and explained in detail in this tutorial for your knowledge.

  1. Find total number of electrons of the valance shells of hydrogen atoms and oxygen atom
  2. Total electrons pairs existing as lone pairs and bonds
  3. Center atom selection
  4. Mark lone pairs on atoms
  5. Mark charges on atoms if there are charges.
  6. Check the stability and minimize charges on atoms by converting lone pairs to bonds to obtain best lewis structure.

Total number of electrons of the valance shells of H3O+

There are two elements in hydronium ion; hydrogen and oxygen. Hydrogen is a group IA element in the periodic table and only has one electron in its last shell (valence shell). Oxygen is a group VIA element in the periodic table and contains six electrons in its last shell. Now, we know how many electrons are there in valence shells of hydrogen and iodine atoms.

  • valence electrons given by hydrogen atom = 1 * 3 = 3
  • valence electrons given by iodine atom = 6 * 1 = 6

  • Due to +1 charge, one electron should be reduced from the total number of valence electrons

  • Total valence electrons = 1 + 7 -1 = 8

Total valence electrons pairs

Total valance electrons pairs = σ bonds + π bonds + lone pairs at valence shells

Total electron pairs are determined by dividing the number total valence electrons by two. For, H3O+ ion, Total pairs of electrons are four in their valence shells.

Center atom of H3O+ ion

Because, hydrogen cannot be a center atom in a molecule or ion, oxygen becomes the center atom.

H3O+ skeleton

Lone pairs on atoms

After determining the center atom and sketch of H3O+ ion, we can start to mark lone pairs on atoms. Remember that, there are total of four electron pairs.

  • There is already three bonds in the drawn skeletal.
  • Usually, those remaining electron pairs should be started to mark on outside atoms. But in H3O+, hydrogen atom cannot keep more than two electron in its last shell. There are already two electrons in hydrogen atom. Therefore, we cannot mark those remaining electrons pairs on hydrogen atom.
  • Therefore, mark those remaining electrons pair on oxygen atom.
mark lone pairs on oxygen aton in H3O+

Mark charges on atoms

There is +1 charge on oxygen atom in the drawn lewis structure.

Check the stability and minimize charges on atoms by converting lone pairs to bonds

Because hydrogen atom cannot make double bonds, we cannot convert lone pair to a bond. Also, there are not enough lone pairs on atom to convert as bonds to reduce charges. That means, we have already obtained the lewis structure.


Lewis Structures of Molecules