The molecular geometry of a water molecule is bent, with the two hydrogen atoms forming an angle around the central oxygen atom.
A water molecule has two O–H bonds and two lone pairs of electrons on oxygen. In VSEPR theory, these four electron regions arrange approximately tetrahedrally, but molecular geometry describes only the positions of atoms, not lone pairs. Because the lone pairs repel the bonding pairs strongly, the hydrogen atoms are pushed together into a bent or V-shaped arrangement.
The H–O–H bond angle is about 104.45°, smaller than the ideal tetrahedral angle of 109.47°. This uneven distribution of charge makes water polar: oxygen carries a partial negative charge, while the hydrogen atoms carry partial positive charges. Polarity helps water form hydrogen bonds and explains many of its unusual physical properties.
A common mistake is calling water tetrahedral. Its electron-pair geometry is often described as tetrahedral, but its molecular geometry is bent. It is not linear because the oxygen atom’s lone pairs prevent the O–H bonds from pointing in opposite directions. Similar bent molecules include sulfur dioxide and nitrogen dioxide.