VSEPR Geometry Calculator

VSEPR theory (Valence Shell Electron Pair Repulsion) is a model used in chemistry to predict the three-dimensional shape of individual molecules based on the electrostatic repulsion between their electron pairs. Developed by Ronald Gillespie and Ronald Sydney Nyholm in 1957, VSEPR theory provides a remarkably simple yet powerful framework for understanding molecular geometry. The central idea is that electron pairs around a central atom arrange themselves as far apart as possible to minimize repulsion, and this arrangement determines the molecule's overall shape.

There are two types of electron pairs to consider: bonding pairs, which are shared between the central atom and surrounding atoms in chemical bonds, and lone pairs (also called non-bonding pairs), which reside solely on the central atom. Both types influence molecular geometry, but lone pairs occupy more space than bonding pairs because they are held closer to the central atom and spread out more. This extra spatial demand means that lone pairs compress bond angles slightly, which is why molecules with the same number of electron domains can have different shapes.

VSEPR theory works in tandem with hybridization theory to provide a complete picture of molecular structure. The steric number — the total count of bonding pairs plus lone pairs on the central atom — determines the electron-pair geometry (the spatial arrangement of all electron domains). The molecular geometry, which describes the actual positions of atoms, is then derived by ignoring the lone pairs and looking only at the atom positions. This calculator lets you input the number of bonding and lone pairs to instantly predict molecular geometry, electron geometry, bond angles, hybridization, and polarity.

In VSEPR notation, a molecule is described using the formula AX_nE_m, where A represents the central atom, X denotes each bonding pair (or bonded atom), and E represents each lone pair on the central atom. The steric number is the sum n + m, which determines the electron-pair geometry. For example, water (H₂O) is classified as AX₂E₂ because oxygen is the central atom bonded to two hydrogen atoms with two lone pairs remaining on the oxygen.

The table below summarizes all common VSEPR geometries for steric numbers 2 through 6. Each combination of bonding and lone pairs produces a unique molecular shape with characteristic bond angles. The hybridization column shows the orbital hybridization that corresponds to each electron geometry.

Follow these steps to predict the geometry of any molecule:

1. Enter Bonding Pairs: Input the number of atoms bonded to the central atom (2–6). For example, methane (CH₄) has 4 bonding pairs around carbon.
2. Enter Lone Pairs: Input the number of non-bonding electron pairs on the central atom (0–3). Water has 2 lone pairs on oxygen, while ammonia has 1 lone pair on nitrogen.
3. View Results: The calculator instantly displays the molecular geometry name, electron geometry, ideal bond angle, orbital hybridization, steric number, and AXₙEₘ notation. You also see example molecules matching that geometry and a polarity prediction.
4. Try Quick Presets: Click on any preset molecule button (CH₄, NH₃, H₂O, CO₂, SF₆, BF₃) to auto-fill the correct bonding and lone pair counts for that well-known molecule.

The calculator validates all combinations against a database of common VSEPR geometries. If you enter a combination that does not correspond to a standard geometry, an informative message is displayed.

The calculator provides several key pieces of information for each geometry. The molecular geometry describes the three-dimensional arrangement of atoms, while the electron geometry describes the arrangement of all electron domains (both bonding and lone pairs). These two geometries are the same when there are no lone pairs; when lone pairs are present, the molecular geometry differs from the electron geometry because lone pairs are invisible in the molecular shape but still influence bond angles.

Bond angles represent the ideal angles between adjacent bonds. Lone pairs compress these angles because they occupy more angular space than bonding pairs. For instance, in a perfect tetrahedron the angle is 109.5°, but ammonia's single lone pair reduces it to approximately 107°, and water's two lone pairs compress it further to about 104.5°. The hybridization (sp, sp², sp³, sp³d, sp³d²) describes which atomic orbitals mix to form the bonding framework.

The polarity prediction indicates whether the molecule is likely polar or nonpolar. Molecules with zero lone pairs and identical surrounding atoms tend to be nonpolar due to symmetric charge distribution. When lone pairs are present or when different types of atoms surround the central atom, the molecule is usually polar because the charge distribution becomes asymmetric. This prediction is a useful first approximation, though full polarity analysis also considers bond dipoles and molecular symmetry.

VSEPR theory is indispensable across many areas of chemistry and materials science. In pharmaceutical chemistry, predicting molecular geometry helps medicinal chemists understand how drug molecules fit into protein binding sites. The three-dimensional shape of a drug determines its ability to interact with biological targets, making VSEPR predictions a starting point for drug design and optimization.

In environmental chemistry, molecular geometry influences how pollutants interact with water, soil, and atmospheric systems. For example, understanding that CCl₄ is tetrahedral and nonpolar explains why it is an effective nonpolar solvent, while the bent shape of SO₂ explains its solubility in water and its role in acid rain formation. In materials science, the geometry of molecules determines packing efficiency in crystals, which affects properties like melting point, density, and optical behavior.

VSEPR predictions are also essential in inorganic chemistry for understanding coordination complexes, where the geometry around a metal center determines magnetic properties, color, and reactivity. Transition metal complexes with octahedral, tetrahedral, or square planar geometries exhibit distinct spectroscopic and magnetic behaviors that can be predicted from their VSEPR geometry.