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ScienceQuest

Water (H₂O) Lewis structure

8 valence electrons, bent

O H H
H₂O as the Lewis Structure Generator draws it: lone pairs as dots.

Build H₂O step by step in the Lewis Structure Generator

What is the Lewis structure of H₂O?

Water, H₂O, has 8 valence electrons. Oxygen is the central atom, joined by two O−H single bonds. It carries two lone pairs on the central O. Every formal charge is zero. O is AX₂E₂: bent, with an ideal bond angle of 109.5°, and the molecule is polar.

Valence electrons in H₂O

Element Group Valence electrons Atoms Electrons
Hydrogen 1 1 2 2
Oxygen 16 6 1 6
Total 8

In one line: 2 × 1 + 6 = 8. Each atom brings the valence electrons its group gives it.

How to draw the H₂O Lewis structure

  1. Count the valence electrons. Valence electrons: each H 1 and O 6. 2 × 1 + 6 = 8.
  2. Choose the central atom. O is the only atom other than H, and H is never in the middle, since it holds only two electrons and so makes one bond.
  3. Join the atoms with single bonds. Two single bonds use 4 electrons, leaving 8 − 4 = 4.
  4. Complete the outer atoms. Every outer atom is H, and its one bond already gives it the two electrons it holds. 4 remain.
  5. Put the rest on the central atom. The 4 left go on the central atom as two lone pairs on O, and O now has 8 electrons round it.
  6. Make multiple bonds where needed. Every atom already has an octet, so no lone pair needs to become a bond.

Lone pairs and formal charges in H₂O

Atom Number Bonds Lone pairs Electrons round it Formal charge, V − N − B/2
O (central) 1 two single bonds 2 8 6 − 4 − 2 = 0
H 2 one single bond 0 2 1 − 0 − 1 = 0

V is the atom’s valence electrons, N its nonbonding electrons and B its bonding electrons. The formal charges add up to 0, the molecule’s overall charge.

Shape and polarity of H₂O

Central atom O
VSEPR class AX₂E₂
Electron geometry tetrahedral
Molecular geometry bent
Ideal bond angle 109.5°
Measured bond angle 104.5°
Polarity, an estimate polar

The bent shape leaves the bond dipoles unbalanced.

O has two σ bonds and two lone pairs, four electron domains in all, so its electron geometry is tetrahedral. Counting only the bonded atoms, the molecular geometry is bent.

The VSEPR Molecular Geometry viewer turns the AX₂E₂ shape in 3D, lone pairs included.

The measured angle is the accepted experimental value the VSEPR viewer quotes for this molecule.

Work with H₂O