Question

What is the geometric structure of the water molecule? How many pairs of valence electrons are there on the oxygen atom in the water molecule? What is the approximate \(\mathrm{H}-\mathrm{O}-\mathrm{H}\) bond angle in water?

Short answer

The geometric structure of the water molecule is bent or V-shaped, due to the repulsion between electron pairs on the oxygen atom. There are four pairs of valence electrons on the oxygen atom (two bonding pairs and two lone pairs). The approximate H-O-H bond angle in the water molecule is 104.5°.

Step-by-step solution

Geometric Structure of the Water Molecule

The water molecule is composed of one oxygen atom bonded to two hydrogen atoms. The geometric structure can be described by its molecular shape. In the case of the water molecule, its shape is called 'bent' or 'V-shaped'. This is because the electron pairs on the oxygen atom repel each other, but the two lone pairs of electrons on the oxygen atom repel the bonding pairs more strongly, leading to those bonding pairs being pushed closer together into a V-shape.

Valence Electron Pairs on the Oxygen Atom

To determine the number of valence electron pairs on the oxygen atom in the water molecule, we can check the electron configuration of oxygen, which is 1s²2s²2p⁴. As oxygen is in Group 16 (or Group VI) of the periodic table, it has six valence electrons. Two of these valence electrons are shared with each hydrogen atom to form the O-H bonds. Therefore, the oxygen atom is left with two lone pairs of electrons on the oxygen atom. In total, there are four pairs of valence electrons (two bonding pairs and two lone pairs).

H-O-H Bond Angle in Water

The approximate H-O-H bond angle in the water molecule can be determined based on the electronic geometry and the molecular shape, which is bent due to the two lone pairs of electrons and two bonding pairs. In a tetrahedral molecule with four equal repulsions, the bond angle would be 109.5°; however, the greater repulsion between the lone pairs of electrons and the bonding pairs in water pushes the H-O-H bond angle to be smaller. The bond angle in the water molecule is approximately 104.5°.