H₂O Lewis Structure

On the central oxygen, count electron domains the VSEPR way: each bonded neighbor is one domain (a double or triple bond still counts as one), and each lone pair is one more. H₂O has 2 bonding domains and 2 lone pairs (AX₂E₂), for 4 electron domains in total.

Those domains arrange to minimize repulsion around the oxygen, so H─O─H is bent with a bond angle of ≈104.5°. Lone pairs on oxygen take space but do not count in the shape name, so the molecular geometry (bent) differs from the electron geometry (tetrahedral).

In VSEPR terms H₂O is AX₂E₂: A is oxygen, X₂ are the two hydrogen bonding domains, and E₂ are the two lone pairs on oxygen. The electron geometry is tetrahedral because four domains need about 109.5° of space; the molecular geometry is bent (sometimes called angular) because only the two hydrogens count in the shape. The usual H–O–H angle is about 104.5°. The same four-domain electron count shows up next to methane and ammonia: CH₄ is AX₄ with no lone pairs (tetrahedral molecule), NH₃ is AX₃E with one lone pair (trigonal pyramidal), and H₂O is AX₂E₂ with two lone pairs (bent). Lone pairs change the shape name; they do not change the four-domain electron geometry.

Why Is H₂O Bent?

H₂O is not linear. Four electron domains surround oxygen: two O–H bonding pairs and two lone pairs. Those domains arrange in a tetrahedral pattern (electron geometry = tetrahedral). The lone pairs occupy two corners of that tetrahedron, so only the two hydrogens remain in the visible shape — and that shape is bent. Electron geometry counts every domain; molecular geometry counts only the atoms. That is why “tetrahedral” and “bent” both appear for water: they answer different questions.

H₂O Bond Angle

The H–O–H bond angle is about 104.5°. The ideal tetrahedral angle is 109.5°. In water the two lone pairs on oxygen repel the bonding pairs more strongly than bonding pairs repel each other, so the angle compresses from 109.5° toward 104.5°. Lone-pair–lone-pair repulsion is strongest, then lone-pair–bonding-pair, then bonding-pair–bonding-pair — that ordering is why water is bent more tightly than the bare tetrahedral ideal.

Each O–H bond is polar: oxygen (electronegativity 3.44) pulls shared electrons harder than hydrogen (2.20), so every bond dipole points toward oxygen. Bond polarity alone does not decide the molecule. If H₂O were linear like CO₂, the two equal dipoles would sit 180° apart and cancel. Oxygen keeps two lone pairs (VSEPR AX₂E₂), so the shape is bent at about 104.5° instead. In that bent geometry the bond dipoles are no longer opposite on one line — they share a component toward the oxygen side of the bend, those components add, and a net molecular dipole remains. H₂O is therefore polar. CO₂ has polar X=O bonds but linear AX₂ geometry, so its dipoles cancel and the molecule is nonpolar. Geometry, not bond polarity alone, makes the difference.

The central oxygen has four electron domains — two O–H bonds plus two lone pairs — so it mixes one 2s orbital with three 2p orbitals into four sp³ hybrids. Two hybrids form the σ bonds to hydrogen; the other two hold the lone pairs. That is why the label is sp³, not sp²: sp² is for three domains (trigonal planar electron geometry), and water has four. The hybrids match the tetrahedral electron geometry and the bent molecular shape, so oxygen in H₂O is described as sp³-hybridized.