[AL CHEM] Covalent bond --- Bond Angle of H20

圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/5/50/Water-2D-labelled.png/160px-Water-2D-labelled.png

Diagram 1: Bond angle representation of water (H2O) [not showing two lone pairs of electron but they should be present]

圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/4/43/Hydroxonium-cation.png/100px-Hydroxonium-cation.png

Diagram 2: 3-D schematic representation of hydronium ion (H3O+) showing one lone pair of electron

圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/1/11/Ammonia-2D-dimensions.png/150px-Ammonia-2D-dimensions.png

Diagram 3: 3-D schematic representation of ammonia (NH3) showing one lone pair of electron

The bond angle (H - O - H) in water is smaller as it has two lone pairs of electrons (not shown in diagrams), which are 'bulky' and forced the H - O - H bond angle to restrain to a smaller angle.
In the case of hydronium ion, one of the two lone pairs is replaced by a O - H bond, thus leaving one lone pair left, as shown in Diagram 2, making it similar to ammonia in Diagram 3. Less number of 'bulky' lone pairs allow H - O - H bond angle to stretch out to a larger angle, and that is, the slight increase in bond angle mentioned.