A water molecule H2O has a bent molecular geometry due to the presence of two lone pairs of electrons on the central oxygen atom. The electron pair geometry of a water molecule is tetrahedral, which has an ideal bond angle of 109.5.However, the presence of the two lone pairs on the oxygen atom causes a repulsion between the electron pairs, which pushes the hydrogen atoms closer together. As a result, the actual bond angle in a water molecule is approximately 104.5, which is smaller than the ideal tetrahedral bond angle of 109.5.