In chemistry, hydronium (hydroxonium in traditional British English) is the cation [H 3 O] +, also written as H 3 O +, the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid is dissolved in water, as Arrhenius acid molecules in solution give up a proton (a positive ...

In the hydronium [H 3 O] + ion, there are 3 single bonds and 1 lone pair around the central oxygen atom which makes a total of 3+1 = 4 electron density regions. Thus, its electron geometry is tetrahedral.

Hydronium not only forms as a result of the dissociation of water, but also forms when water is in the presence of an acid. As the acid dissociates, the H + ions bond with water molecules to form hydronium, as seen here when hydrochloric acid is in the presence of water: \[HCl (aq) + H_2O \rightarrow H_3O^+ (aq) + Cl^-(aq)\]

From the above chart, we can see that hydronium ion is a AX3E type molecule (A= central atom, X= bonded atom, E= lone pair on A). So according to the VSEPR chart, H3O+ has trigonal pyramid as its molecular shape and tetrahedral as its electron geometry.

In chemistry, hydronium or the hydronium ion refers to the chemical species H 3 O +. Hydronium is the simplest oxonium ion, where an oxonium ion is any oxygen cation having three chemical bonds. The International Union of Pure and Applied Chemistry (IUPAC) recommends the term “oxonium” or “hydroxonium” be used in place of the word ...