Molecule Builder
Drag atoms into the workspace, connect them with covalent bonds, and watch the molecular formula, valence status, molar mass, Lewis structure and geometry update live — a small virtual chemistry lab, not a formula calculator.
Atom Library
Drag an atom onto the canvas, or click/tap it to add it near the center.
Understanding Molecules & Bonding
Use these references alongside the builder above to connect what you’re constructing with the underlying chemistry.
What is a molecule?
A molecule is two or more atoms held together by chemical bonds, forming the smallest unit of a chemical compound that still has that compound's properties. It can be made of the same element (like O₂) or different elements (like H₂O).
How are molecules formed?
Molecules form when atoms share or transfer valence electrons to reach a more stable, lower-energy electron arrangement — most commonly by sharing electron pairs in covalent bonds, which is what this tool lets you build and explore.
What is a covalent bond?
A covalent bond is a chemical bond formed when two atoms share one or more pairs of electrons, so both atoms experience the pull of both nuclei. It typically forms between nonmetal atoms with similar electronegativities.
What is the difference between single, double, and triple bonds?
A single bond shares one electron pair (C–C), a double bond shares two pairs (C=C), and a triple bond shares three pairs (C≡C). More shared pairs mean a shorter, stronger bond, but also less freedom to rotate around that bond axis.
What are valence electrons?
Valence electrons are the electrons in an atom's outermost shell — the ones available to form bonds with other atoms. The number of valence electrons largely determines how many bonds an atom typically forms and its position on the periodic table.
What is a Lewis structure?
A Lewis structure is a diagram that shows how valence electrons are arranged in a molecule: as bonding pairs (shared between atoms, drawn as lines) and lone pairs (unshared, drawn as dots). Toggle "Lone Pairs" in the builder to see them.
What is molecular geometry?
Molecular geometry is the actual 3D arrangement of a molecule's atoms in space — for example bent, linear, tetrahedral, or trigonal pyramidal — which a flat 2D Lewis structure alone cannot fully show. Use the 3D viewer to explore it.
What is VSEPR theory?
VSEPR (Valence Shell Electron Pair Repulsion) theory predicts molecular geometry by assuming that electron domains around a central atom — both bonding pairs and lone pairs — arrange themselves as far apart as possible to minimize repulsion.
What makes a molecule polar or nonpolar?
A molecule is polar if it has a net dipole moment — which depends on both how polar its individual bonds are (from electronegativity differences) and its overall geometry. CO₂ has polar bonds but is nonpolar overall because its linear, symmetric shape cancels the bond dipoles; water's bent shape does not, so it stays polar.