How to build a molecule
Every molecule is just specific atoms in specific counts, joined by chemical bonds. Tap atoms from the palette into your tray, and the running count shows what you have. Get the right atoms (say two hydrogen and one oxygen) and press Bond them!: they snap into the real Lewis structure and you see its shape and polarity. Then the builder shows you the standard way to write the formula (H₂O, NH₃), and if you happened to place the atoms in that order, it gives you a little extra credit. Same molecule either way; the order is just how chemists spell it.
- Challenge mode names a target (“Build water, H₂O”) and you assemble it. Each one you finish adds to your score.
- Sandbox mode lets you free-build. Find a real molecule and it joins your collection. Can you discover all 42?
Sandbox never leaves you stuck. If your atoms don’t make anything yet, the builder works out the closest molecule it knows and tells you what to change: put a carbon and three hydrogens in the tray and it will say you are one hydrogen short of methane. Being one atom away from something real is the most useful moment in the whole exercise, so it is worth saying out loud.
Why building beats memorizing
Snapping atoms together turns abstract formulas into something you do. You quickly feel why H₂O needs two hydrogens and one oxygen, why CO₂ is built from one carbon and two oxygens, and how the same handful of atoms recombine into very different molecules. That hands-on intuition is exactly what makes Lewis structures and molecular shapes click later.
The clearest lesson in the whole set is the methane series. Build CH₄, then CH₃Cl, CH₂Cl₂, CHCl₃, and CCl₄ in turn. Every one is a tetrahedron with the same 109.5° angles, yet only the two with four identical corners come out nonpolar. Shape alone does not decide polarity; what sits on the corners does.
From atoms to bonds to shape
When you bond atoms, the builder shows the finished molecule’s geometry and whether it’s polar: the payoff of the whole bonding story:
- Which atoms bond, and how many, comes from each atom’s valence electrons.
- Whether a bond is ionic or covalent depends on electronegativity.
- The finished molecule’s shape follows VSEPR, and its polarity depends on whether the bond dipoles cancel.
Build a familiar one to start: try hydrogen and oxygen for water, or carbon and oxygen for carbon dioxide.
Every molecule you can build
These are all the molecules in the builder, with the atoms each one needs. The shapes and bond angles are the measured ones, and the builder draws each structure from this same data, so what you see when it snaps together matches the table.
| Formula | Name | Atoms | Shape | Bond angle | Polarity |
|---|---|---|---|---|---|
| H₂O | Water | 2 H + 1 O | bent | 104.5° | Polar |
| CO₂ | Carbon dioxide | 1 C + 2 O | linear | 180° | Nonpolar |
| NH₃ | Ammonia | 3 H + 1 N | trigonal pyramidal | 107° | Polar |
| CH₄ | Methane | 1 C + 4 H | tetrahedral | 109.5° | Nonpolar |
| CCl₄ | Carbon tetrachloride | 1 C + 4 Cl | tetrahedral | 109.5° | Nonpolar |
| BF₃ | Boron trifluoride | 1 B + 3 F | trigonal planar | 120° | Nonpolar |
| CH₂O | Formaldehyde | 1 C + 2 H + 1 O | trigonal planar | 120° | Polar |
| HCN | Hydrogen cyanide | 1 C + 1 H + 1 N | linear | 180° | Polar |
| PCl₅ | Phosphorus pentachloride | 5 Cl + 1 P | trigonal bipyramidal | 90° & 120° | Nonpolar |
| SF₆ | Sulfur hexafluoride | 6 F + 1 S | octahedral | 90° | Nonpolar |
| HCl | Hydrogen chloride | 1 Cl + 1 H | linear | - | Polar |
| HF | Hydrogen fluoride | 1 F + 1 H | linear | - | Polar |
| O₂ | Oxygen | 2 O | linear | - | Nonpolar |
| N₂ | Nitrogen | 2 N | linear | - | Nonpolar |
| H₂ | Hydrogen | 2 H | linear | - | Nonpolar |
| F₂ | Fluorine | 2 F | linear | - | Nonpolar |
| Cl₂ | Chlorine | 2 Cl | linear | - | Nonpolar |
| CO | Carbon monoxide | 1 C + 1 O | linear | - | Polar |
| CS₂ | Carbon disulfide | 1 C + 2 S | linear | 180° | Nonpolar |
| H₂S | Hydrogen sulfide | 2 H + 1 S | bent | 92° | Polar |
| SCl₂ | Sulfur dichloride | 2 Cl + 1 S | bent | 103° | Polar |
| OF₂ | Oxygen difluoride | 2 F + 1 O | bent | 103° | Polar |
| SO₂ | Sulfur dioxide | 2 O + 1 S | bent | 119° | Polar |
| SO₃ | Sulfur trioxide | 3 O + 1 S | trigonal planar | 120° | Nonpolar |
| BCl₃ | Boron trichloride | 1 B + 3 Cl | trigonal planar | 120° | Nonpolar |
| PH₃ | Phosphine | 3 H + 1 P | trigonal pyramidal | 93.5° | Polar |
| PCl₃ | Phosphorus trichloride | 3 Cl + 1 P | trigonal pyramidal | 100° | Polar |
| NF₃ | Nitrogen trifluoride | 3 F + 1 N | trigonal pyramidal | 102° | Polar |
| SiH₄ | Silane | 4 H + 1 Si | tetrahedral | 109.5° | Nonpolar |
| CF₄ | Carbon tetrafluoride | 1 C + 4 F | tetrahedral | 109.5° | Nonpolar |
| CH₃Cl | Chloromethane | 1 C + 3 H + 1 Cl | tetrahedral | 109.5° | Polar |
| CH₂Cl₂ | Dichloromethane | 1 C + 2 H + 2 Cl | tetrahedral | 109.5° | Polar |
| CHCl₃ | Chloroform | 1 C + 1 H + 3 Cl | tetrahedral | 109.5° | Polar |
| XeF₂ | Xenon difluoride | 2 F + 1 Xe | linear | 180° | Nonpolar |
| SF₄ | Sulfur tetrafluoride | 4 F + 1 S | seesaw | 173° & 102° | Polar |
| ClF₃ | Chlorine trifluoride | 1 Cl + 3 F | T-shaped | 87.5° | Polar |
| XeF₄ | Xenon tetrafluoride | 4 F + 1 Xe | square planar | 90° | Nonpolar |
| BrF₅ | Bromine pentafluoride | 1 Br + 5 F | square pyramidal | 84.8° | Polar |
| HBr | Hydrogen bromide | 1 Br + 1 H | linear | - | Polar |
| HI | Hydrogen iodide | 1 H + 1 I | linear | - | Polar |
| Br₂ | Bromine | 2 Br | linear | - | Nonpolar |
| I₂ | Iodine | 2 I | linear | - | Nonpolar |
A few are worth building back to back. H₂O and H₂S are the same bent shape with a very different angle. NH₃ and NF₃ are the same pyramid, yet ammonia is strongly polar and nitrogen trifluoride barely is. SO₂ and CO₂ look like they should match and do not: sulfur keeps a lone pair, so SO₂ bends and is polar while CO₂ stays linear and is not.
Use it in class
Project it and have students race to build a target, or challenge them to discover every molecule in sandbox mode. It’s free to embed on your own site or LMS: one line of code, no signup.