Water: Bent Molecular Geometry

The oxygen has 6 valence electrons and thus needs 2 more electrons from 2 hydrogen atoms to complete its octet. This then leaves two lone electron pairs that are not bonded to any other atoms. The two hydrogen atoms and the two lone electron pairs are as far apart as possible at nearly 109^o bond angle. This is tetrahedral electron pair geometry.

The 2 lone electron pairs exerts a little extra repulsion on the two bonding hydrogen atoms to create a slight compression to a 104^obond angle.The water molecule is bent molecular geometry because the lone electron pairs, although still exerting influence on the shape, are invisible when looking at molecular geometry. The molecule is two dimensional and bent as opposed to the beryllium hydride case which was a linear or straight line molecular geometry because it did not have a lone electron pair.