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Why does a water molecule have a bent shape?

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Diagram showing four types of crystal bonding: ionic bonding with sodium and chlorine ions, covalent bonding with carbon atoms sharing electrons, metallic bonding with iron ions surrounded by free electrons, and molecular bonding with hydrogen molecules held by weak electrical attraction. — chemical bonding Different types of bonding in crystals.

The water molecule ( $H_{2} O$ ) has a bent shape due to the arrangement of electron pairs around the central oxygen atom, as explained by VSEPR theory.

The oxygen atom in water is surrounded by four electron pairs: two bonding pairs connected to hydrogen atoms and two lone pairs of unshared electrons. According to VSEPR theory, these four pairs adopt a tetrahedral arrangement to maximize their separation from one another.1

While the electron pairs are arranged tetrahedrally, the actual shape of the molecule is determined by the positions of the atoms. Because the two lone pairs occupy more space than the bonding pairs, they exert greater repulsive forces. This causes the lone pairs to push the bonding pairs closer together, resulting in a bond angle of approximately 104.5° rather than the ideal tetrahedral angle of 109.5°. Consequently, the molecule is described as angular or bent.21