VSEPR Molecular Shapes (3D)
Valence Shell Electron Pair Repulsion (VSEPR) predicts three-dimensional arrangements of electron domains (bonding pairs and lone pairs) around a central atom. The **steric number** is the count of those domains; it sets the **electron geometry** (linear, trigonal planar, tetrahedral, trigonal bipyramidal, or octahedral for two through six domains). **Molecular shape** describes where the bonded atoms actually sit once lone pairs—often modeled as slightly larger, more repulsive regions—occupy some of those directions. This lab shows an idealized **ball-and-stick plus translucent lone-pair lobes** sketch: domain vectors are fixed to symmetric polyhedra, and lone pairs follow simplified textbook placement rules (for example, lone pairs prefer equatorial sites on a trigonal bipyramid to reduce 90° crowding; two lone pairs on an octahedron are shown trans to each other so the four bonds lie in a plane). Sliders change the AXₙEₘ counts; presets recall common textbook examples such as CO₂, H₂O, NH₃, CH₄, PCl₅, SF₆, XeF₂, and XeF₄. The model is **pedagogical**, not a quantum geometry optimization: real bond angles differ when electronegativity and π bonding matter, and some hypervalent molecules need molecular-orbital ideas beyond first-year VSEPR cartoons.
Who it's for: High school and first-year college general chemistry students learning VSEPR tables, AXE notation, and the distinction between electron geometry and molecular shape before Walsh diagrams or computational structure.
Key terms
- VSEPR theory
- Steric number
- Electron geometry
- Molecular shape
- AXE notation
- Lone pair repulsion
- Trigonal bipyramid
- Octahedral geometry
- Square planar
How it works
Valence Shell Electron Pair Repulsion (VSEPR) predicts **electron geometry** from the steric number (bonding + lone pairs) and **molecular shape** from where atoms actually sit. Rotate the 3D model to compare textbook angles with this idealized ball-and-lone-pair sketch (not a quantum geometry optimization).
Key equations
Frequently asked questions
- Why do lone pairs look like purple clouds instead of atoms?
- They are a visualization of non-bonding valence electron density occupying direction around the central atom. The simulator does not draw orbitals; it marks directions where lone pairs are assumed to repel bonded pairs more strongly than bond–bond repulsion alone would suggest.
- Are the bond angles exact numbers like 109.5°?
- Only for perfect tetrahedral, octahedral, or trigonal bipyramidal reference geometry. The scene uses symmetric unit vectors; real molecules (H₂O, NH₃, etc.) deviate because lone pairs are not identical to bonds and electronegativity pulls electron density. Compare this page to quantitative experiments or quantum calculations when precision matters.
- Why does XeF₂ use two bonds and three lone pairs on xenon?
- It is a hypervalent example where the steric number is five (trigonal bipyramidal electron geometry) but three equatorial sites are lone pairs so the two fluorines sit on opposite axial positions—giving a **linear molecular shape** for the nuclei.
- Does this replace a full molecular viewer?
- No. The Molecule Viewer lab shows real coordinates for specific compounds. Here the goal is to connect **counts** of bonding and lone pairs to **named geometries** and to practice AXₙEₘ reasoning independent of a particular bond length.
More from Chemistry
Other simulators in this category — or see all 21.
Galvanic (Voltaic) Cell
Two half-cells, salt bridge, voltmeter; E°cell and Nernst E from ion concentrations (pedagogical E°).
Hess's Law (Enthalpy Paths)
Two-step vs direct ΔH on an enthalpy diagram; sum must match declared overall ΔH.
Unit Cell SC / BCC / FCC
Conventional cubic cells; yaw–pitch projection — lattice sites before basis detail.
Sequential Stern–Gerlach
Two SG devices: P(up on SG₂) = cos²(θ/2) or sin²(θ/2) after |±z⟩ filter.
Molecule Viewer (3D)
Common molecules in 3D. Rotate, zoom. Ball-and-stick models.
Periodic Table
Click element for properties, electron config, and uses.