Lewis Structure Generator & VSEPR Theory Calculator
Generate Lewis dot structures, predict molecular geometry using VSEPR theory, calculate bond angles, and analyze molecular polarity.
Generate Lewis Structure
Enter formula like H2O, CO2, NH3, or use generic notation (ML₂, AX₃, MX₄, etc.)
H₂O (Water)
CO₂ (Carbon Dioxide)
NH₃ (Ammonia)
CH₄ (Methane)
O₂ (Oxygen)
N₂ (Nitrogen)
SO₂ (Sulfur Dioxide)
HCN (Hydrogen Cyanide)
C₂H₄ (Ethylene)
PCl₃ (Phosphorus Trichloride)
ML₂ (Generic)
AX₃ (Generic)
MX₄ (Generic)
For ions: +1 for cation, -1 for anion
VSEPR Geometry Predictor
Count single, double, and triple bonds as 1 bonding region each
2B-0LP (Linear)
3B-0LP (Trigonal Planar)
2B-1LP (Bent)
4B-0LP (Tetrahedral)
3B-1LP (Trigonal Pyramidal)
2B-2LP (Bent)
5B-0LP (Trigonal Bipyramidal)
6B-0LP (Octahedral)
Formal Charge Calculator
Formula: Formal Charge = (Valence e⁻) - (Non-bonding e⁻) - (Bonding e⁻ / 2)
C=4, N=5, O=6, H=1, etc.
Single bond = 2, Double = 4, Triple = 6
Understanding Lewis Structures
What are Lewis Structures?
Lewis structures (or Lewis dot diagrams) are visual representations of molecules showing:
- Bonding electrons as lines between atoms (each line = 2 electrons)
- Lone pairs as dots around atoms
- Formal charges when electron distribution differs from neutral atoms
Steps to Draw Lewis Structures
- Count valence electrons: Add up all valence electrons (adjust for charge)
- Arrange atoms: Least electronegative in center (H always terminal)
- Draw single bonds: Each bond uses 2 electrons
- Complete octets: Distribute remaining electrons (8 for most, 2 for H)
- Form multiple bonds: If needed to satisfy octet rule
- Check formal charges: Best structure has charges closest to zero
VSEPR Theory
Valence Shell Electron Pair Repulsion (VSEPR) theory predicts 3D molecular geometry based on:
- Electron pairs repel each other and arrange to minimize repulsion
- Both bonding pairs and lone pairs count as "electron domains"
- Lone pairs occupy more space than bonding pairs
Common Geometries
| Steric # | Bonds | Lone Pairs | Molecular Geometry | Bond Angle | Example |
|---|---|---|---|---|---|
| 2 | 2 | 0 | Linear | 180° | CO₂ |
| 3 | 3 | 0 | Trigonal Planar | 120° | BF₃ |
| 3 | 2 | 1 | Bent | <120° | SO₂ |
| 4 | 4 | 0 | Tetrahedral | 109.5° | CH₄ |
| 4 | 3 | 1 | Trigonal Pyramidal | <109.5° | NH₃ |
| 4 | 2 | 2 | Bent | <109.5° | H₂O |
| 5 | 5 | 0 | Trigonal Bipyramidal | 90°, 120° | PCl₅ |
| 6 | 6 | 0 | Octahedral | 90° | SF₆ |
Formal Charge Rules
- The best Lewis structure has formal charges closest to zero
- Negative formal charges should be on more electronegative atoms
- Adjacent atoms should not have same-sign formal charges
- Minimize the number of atoms with non-zero formal charges
Exceptions to Octet Rule
- Incomplete octets: H (2e⁻), Be (4e⁻), B (6e⁻)
- Expanded octets: Period 3+ elements can use d-orbitals (P, S, Cl, etc.)
- Odd-electron molecules: Free radicals like NO, NO₂