Lewis Dot Structure Builder

Enter a molecular formula to generate its Lewis structure with bonds, lone pairs, and VSEPR geometry prediction. See step-by-step valence electron counting and shape classification.

Lewis Structure

Molecular Formula

Enter formula (e.g. H2O, CO2, NH3)

Presets

Results

Central Atom

O

Total Valence Electrons

8

Steric Number

4

Lone Pairs on Central

2

Electron Geometry

Tetrahedral

Molecular Shape

Bent

Bond Angle

~104.5°

Bond Orders

O-H (single)O-H (single)

Step-by-Step

1. Count total valence electrons

\text{Total} = 2 \times 1\text{ (H)} + 6\text{ (O)} = 8

2. Draw single bonds to each outer atom

\text{2 bonds} \times 2 = 4\text{ electrons used}

3. Remaining electrons

8 - 4 = 4\text{ electrons}

4. Distribute lone pairs to outer atoms (satisfy octets)

\text{Remaining after outer atoms: }4\text{ electrons}

5. Place remaining electrons on central atom

\text{Central atom (O) gets }2\text{ lone pairs}

6. VSEPR geometry

\text{Steric number} = 2\text{ bonding} + 2\text{ lone} = 4

7. Molecular shape

\text{Electron geometry: Tetrahedral, Molecular shape: Bent, Bond angle: ~104.5°}

Reference Guide

Valence Electrons

Valence electrons are the outer-shell electrons that participate in bonding. The group number in the periodic table tells you how many each element has.

\text{C: 4, N: 5, O: 6, F: 7, H: 1}

The Octet Rule

Most atoms seek 8 electrons in their valence shell (2 for hydrogen). Bonds and lone pairs are arranged to satisfy this rule.

VSEPR Theory

Valence Shell Electron Pair Repulsion theory predicts molecular geometry. Electron pairs around the central atom spread out to minimize repulsion.

Bond Angles

Common geometries and their ideal bond angles include tetrahedral (109.5), trigonal planar (120), and linear (180). Lone pairs compress bond angles slightly.