H3O+ Molecular Geometry / Shape and Bond Angles

A quick explanation of the molecular geometry of H3O+ (the Hydronium ion) including a description of the H3O+ bond angles.

Looking at the H3O+ Lewis structure we can see that there are three atoms attached to the central Oxygen (O) atom as well as a lone pair of electrons.  Based on VSEPR Theory (Valence Shell Electron Pair Repulsion Theory) the electron clouds on atoms and lone pair of electrons around the O atom will repel each other.  As a result they will be pushed apart giving the H3O+ molecule a trigonal pyramidal molecular geometry or shape.

The H3O+ bond angle will be about 109.5 degrees since it has a trigonal pyramidal molecular geometry (it will be a bit less since the lone pair will push down – the actual value is approximately 113 degrees).
--How to Determine the Molecular Geometry--

1) Draw the Lewis Structure for the compound.
2) Predict how the atoms and lone pairs will spread out when the repel each other.
3) Use a chart based on steric number (like the one in the video) or use the AXN notation to find the molecular shape. This will be determined by the number of atoms and lone pairs attached to the central atom.

Helpful Resources:
• How to Draw Lewis Structures: How to Draw Lewis Structures: Five Ea...
• Molecular Geometry and VSEPR Explained: Molecular Geometry: Rules, Examples, ...
• Molecular Geo App: https://phet.colorado.edu/sims/html/m...

Get more chemistry help at http://www.breslyn.org

Drawing/writing done in InkScape. Screen capture done with Camtasia Studio 4.0. Done on a Dell Dimension laptop computer with a Wacom digital tablet (Bamboo).

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