Question

What is the structure of hydronium ion ${{\text{H}}_{\text{3}}}{{\text{O}}^ + }$?

Answer 1

Hint: We know that in the hydronium ion, three hydrogen atoms are bonded to the oxygen atom. Also, there is one lone pair of electrons on the oxygen atom. A pair of electrons that occupies the orbital of the atom but is not involved in the bonding directly is known as a lone pair of electrons.

Complete answer:

The molecular formula for the hydronium ion is ${{\text{H}}_{\text{3}}}{{\text{O}}^ + }$.

The hydronium ion is formed when the water molecule reacts with a hydrogen ion.

The reaction is as follows:

${{\text{H}}_{\text{2}}}{\text{O}} + {{\text{H}}^ + } \to {{\text{H}}_{\text{3}}}{{\text{O}}^ + }$

The hydrogen ion does not have any electrons. The oxygen atom in the water molecule has two lone pairs of electrons. Thus, the oxygen atom shares one of its lone pairs and forms the coordinate covalent bond. Thus, the coordinate bond is present in the hydronium ion.

The structure of hydronium ion is as follows:

From the structure of the hydronium ion, we can see that there are three bonding pairs of electrons and one lone pair of electrons.

The molecules or ions having three bonding pairs and one lone pair have pyramidal structure.

Thus, the structure of the hydronium ion is pyramidal. This is because it has three bonding pairs of electrons and one lone pair of electrons. The bond angle is ${107^ \circ }$.

Note: If there would not have been any lone pair, the structure of the hydronium ion would be trigonal planar. The molecules or ions having three bond pairs of electrons and no lone pair have trigonal planar structures.