Structures in 3D sim

What the sim shows

Each model is a small piece of a structure that goes on and on in every direction (iodine is a crystal of separate molecules). Balls are drawn smaller than the real atoms and ions so the bonds can be seen; Na⁺ and Cl⁻, and copper and tin, keep their true size ratio. Distances, melting points and the heat data for iodine are standard data-book values, rounded. Idealised, and the desk's choice: silicon dioxide is drawn as ideal cristobalite (each Si–O–Si straight; in quartz it bends to about 144°, with the same 4 and 2 count); the iodine molecules sit in a simple herringbone with the real bond length and closest contacts; bronze has 1 tin ion in every 8 (bell bronze, about 22% tin by mass). The thin rods in sodium chloride stand for the pull between neighbouring ions, not shared electrons. The metal's layers slide along the easy zig-zag path, over the gaps between the ions below. In the alloy, the push stops at the first gap with a tin ion in it: that is the lesson's rule. Hard balls alone would still pass; in a real alloy the bigger ions bend the rows round them, and the bent rows catch the sliding layer. Electrons and the heating are shown faster than real life. Each structure is drawn to its own scale.

Use it in your lessons

• Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
• Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
• Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.

Free guide: 12 practicals as sims, and how to run one in a lesson →

Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.