# VSEPR Calculator - Molecular Geometry, Hybridization, Bond Angles and 3D Model

> Free VSEPR calculator: enter SF4, NH4+ or SO4^2- for the steric number, lone pairs, AXE notation, electron and molecular geometry, angles and hybridization.

- URL: https://qilingtools.com/en/math/vsepr
- Category: Chemistry Tools (https://qilingtools.com/en/chemistry)
- Tags: [Chemistry](https://qilingtools.com/en/tags/chemistry), [Education](https://qilingtools.com/en/tags/education)
- Last updated: 2026-10-26
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the shape of a molecule from the electron domains — bonding pairs and lone pairs — around its central atom, which arrange themselves as far apart as possible. The lone pairs on the central atom are (a − Σb)/2, where a is the central atom's valence electrons (minus the charge for a cation, plus it for an anion) and b is the number of electrons each surrounding atom still needs (1 for H and halogens, 2 for O and S, 3 for N); the steric number is the number of bonded atoms plus lone pairs. For SF₄: a = 6, four F atoms need 1 each, so there is (6 − 4)/2 = 1 lone pair and a steric number of 5. The electron-domain geometry is trigonal bipyramidal, the lone pair sits equatorial, and the molecule is a seesaw (AX₄E), sp³d hybridized and polar. Type a formula — ions such as NH4+, SO4^2-, CO3^2- and I3- work too — and the tool picks the central atom (the least electronegative unique atom, or choose your own), then reports total valence electrons, lone pairs, steric number, AXE notation, electron and molecular geometry, ideal and measured bond angles, hybridization and polarity. It also lists bond orders and formal charges from the minimum-formal-charge Lewis structure (terminal O double-bonded; a multiple bond counts as one domain), draws a rotatable 3D ball-and-stick model with CPK colours and lone-pair lobes, and shows a gallery of every VSEPR shape. H atoms in oxoacids are placed on oxygen (–OH).

## How to use

1. Enter a molecule or ion such as SF4, XeF4, NH4+ or SO4^2-, or click an example
2. Read the lone pairs, steric number, AXE class, shape, bond angles, hybridization and polarity; override the central atom if needed
3. Drag the 3D model to rotate it, follow the working, or click a shape in the gallery

## Features

- Lone pairs and steric number by the (a − Σb)/2 method, with full working
- Every common shape from AX2 to AX7: linear, trigonal planar, bent, tetrahedral, trigonal pyramidal, trigonal bipyramidal, seesaw, T-shaped, octahedral, square pyramidal, square planar and more
- Polyatomic ions: NH4+, H3O+, NO3-, CO3^2-, SO4^2-, PO4^3-, I3-
- Minimum-formal-charge Lewis structure: bond order, formal charge and lone pairs per bond
- Hybridization (sp to sp³d²) and polarity
- Ideal bond angles plus measured angles for H2O, NH3, SO2, SF4 and others
- Rotatable 3D ball-and-stick model with translucent lone-pair lobes
- Gallery of all VSEPR geometries that loads a typical example

## FAQ

### How do I find the steric number?

Steric number = atoms bonded to the central atom + lone pairs on the central atom. Lone pairs = (a − Σb)/2, where a is the central atom's valence electrons adjusted for charge and b is what each ligand needs (H and halogens 1, O and S 2, N 3). For SO₄²⁻, a = 6 + 2 = 8 and four O need 2 each, so there are no lone pairs and the steric number is 4 (tetrahedral). For NH₃, (5 − 3)/2 = 1 lone pair, steric number 4, trigonal pyramidal. Double and triple bonds count as one domain.

### Why are the bond angles in NH3 and H2O smaller than 109.5°?

A lone pair is held by only one nucleus, so it sits closer to the central atom and takes up more room than a bonding pair. Repulsion falls in the order lone–lone > lone–bond > bond–bond, so lone pairs squeeze the bonds together: CH₄ (no lone pairs) is 109.5°, NH₃ (one) is about 107° and H₂O (two) about 104.5°. Likewise SO₂ is about 119° instead of 120° and ClF₃ about 87.5° instead of 90°.

### Why do lone pairs go in equatorial positions in SF4, ClF3 and XeF2?

In a trigonal bipyramid an axial position has three neighbours at 90°, while an equatorial position has only two. Putting lone pairs equatorial minimises the strong 90° repulsions, so SF₄ (one lone pair) is a seesaw, ClF₃ (two) is T-shaped, and XeF₂ and I₃⁻ (three) fill all the equatorial positions with lone pairs, leaving a linear molecule.

### How can I tell whether a molecule is polar?

Check whether the shape is symmetric and whether the surrounding atoms are identical. AX₂, AX₃, AX₄, AX₅ and AX₆ species with identical ligands (CO₂, BF₃, CH₄, PCl₅, SF₆), and shapes whose lone pairs cancel such as XeF₂ (linear) and XeF₄ (square planar), have no net dipole and are nonpolar. An unsymmetrical lone pair (NH₃, H₂O, SO₂, SF₄) or different ligands (CH₂Cl₂, POCl₃, HCN) make a molecule polar.

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