Predict the Lewis dot structure and VSEPR molecular geometry of a covalent molecule, step by step.
What you give it. A molecular formula like H2O, CO2, NH3, CH4, SF6, PCl5, XeF4, or SO2. You can also specify the central atom (the tool will pick the least electronegative one if you don't) and the overall charge (for polyatomic ions like SO4^2- or NH4+).
How it works.
- Valence electron count. Sum the valence electrons of every atom (from the periodic table), then add one electron for each negative charge (or subtract for positive).
- Central atom. Usually the least electronegative atom (excluding H, which is always terminal). For example, in
SO2 sulfur is central, not oxygen.
- Skeleton. Place the central atom in the middle, terminal atoms around it, connected by single bonds.
- Octet completion. Distribute the remaining electrons to terminal atoms first (to complete their octets — 2 for H, 8 for everything else), then any leftover to the central atom.
- Multiple bonds. If the central atom lacks an octet, convert terminal lone pairs into double or triple bonds (typically C, N, O, S).
- Formal charges. Compute for every atom; if a lower-charge arrangement exists, suggest it.
- VSEPR. Count bonding regions and lone pairs on the central atom → look up the
AX_nE_m type → report the electron-domain geometry, the molecular shape, and the ideal bond angle.
Geometry table covered. Linear (AX2), Trigonal planar (AX3), Tetrahedral (AX4), Trigonal bipyramidal (AX5), Octahedral (AX6), plus the lone-pair variants: Bent (AX2E / AX2E2), Trigonal pyramidal (AX3E), Seesaw (AX4E), T-shape (AX3E2), Square pyramidal (AX5E), Square planar (AX4E2).
Teaching notes. Each result shows the full reasoning: how many valence electrons, which atom is central and why, how many lone pairs end up where, and the VSEPR type. This is the part students actually need.
Scope & limits. This tool handles main-group covalent molecules and common ions with a single central atom — the standard first-year chemistry curriculum. It does not handle hypervalent oddities, radicals, transition-metal complexes, resonance beyond a note, or multi-center bonding (e.g. boranes). For those, a chemistry textbook or a quantum-chemistry tool is the right answer.