Molecule Builder

How to play

Tap an atom in the tray and it joins the molecule at the glowing yellow spot, or drag it onto any open spot. The stubs on each atom show how many more bonds it can make: hydrogen 1, oxygen 2, nitrogen 3, carbon 4 and chlorine 1. When every bond is full the molecule is complete: double and triple bonds appear where they are needed, and the molecule pops into its real 3D shape, with its lone pairs of electrons shown as purple clouds. Drag to spin it, and tap it to stop or start it turning. Tap an outer atom (or drag it out of the dark box) to take it off. Undo takes back your last change and New clears the board.

Things to try

• Make water, then turn it into hydrogen peroxide (H₂O₂). What did you add?
• Make carbon dioxide and look for the double bonds. Why does the carbon need them?
• Make the three molecules with two carbons: ethane, ethene and ethyne. How are their bonds different?
• Make ethanol, then use the same atoms to make dimethyl ether. Same formula, different molecule.
• Compare methane, ammonia and water. Why do their angles get smaller?
• Make nitrogen gas (N₂) and count the bonds between the two atoms.
• Fill in all 17 squares of the collection.

Teaching molecules?

The Physical and Chemical Changes teaching pack has lesson slides, practice sheets and every answer key for grades 5 to 8, and the Parts of an Atom teaching pack is free by email. Start with the Atom Builder to build the atoms themselves, and print the periodic table. Then balance whole reactions with Balancing Equations.

Questions

What is a molecule?

A molecule is two or more atoms held together by sharing electrons. Water is a molecule of two hydrogen atoms and one oxygen atom (H₂O). An oxygen molecule in the air is two oxygen atoms (O₂).

Why does carbon make 4 bonds but hydrogen only 1?

Atoms share electrons until their outer shell is full. Hydrogen needs 1 more electron, so it makes 1 bond. Oxygen needs 2, nitrogen 3 and carbon 4. Chlorine needs 1. The stubs on each atom in the game show how many bonds it makes.

What are double and triple bonds?

A single bond is one shared pair of electrons. When two atoms share two pairs it is a double bond, and three pairs is a triple bond. In carbon dioxide each oxygen shares two pairs with the carbon (O=C=O), and the two atoms in nitrogen gas share three pairs (N≡N). The game works out where they go once every bond can be filled.

Why is water bent but carbon dioxide straight?

Electron pairs push each other as far apart as they can. The oxygen in water has two pairs of electrons it does not share (lone pairs) as well as its two bonds, and those four groups push the hydrogens down into a bent shape at 104.5°. The carbon in carbon dioxide has no lone pairs and just two groups (its two double bonds), so they point straight out on opposite sides at 180°.

What shapes can molecules have?

With the atoms in this game you will find a straight line (carbon dioxide, 180°), a flat triangle (formaldehyde, 120°), a tetrahedron (methane, 109.5°), a pyramid (ammonia, 107°) and bent (water, 104.5°). The shape comes from how many bonds and lone pairs the middle atom has. This idea is called VSEPR.

Why can't I make ozone or rings?

This game builds molecules as branches: each new atom joins one atom already there. That covers most simple molecules, but not rings like benzene, and not ozone (O₃), whose real structure needs charged atoms. Those may come in a later version.

Are these molecules real?

Every named molecule is real, with its real shape and bond angles. If every bond is full but the molecule is not one we know, the game tells you its formula. If it has a chain of three or more oxygen or nitrogen atoms, the game says so, because those fall apart.

Is it really free?

Yes. No sign-up, no ads. Your molecule and the ones you have made are saved on this device.