Atom Builder (Isotopes & Ions)
Build atoms from protons, neutrons and electrons and see the element, isotope and charge.
Drag protons, neutrons and electrons from the buckets into the atom. Protons and neutrons go in the nucleus and electrons go on the rings. See which element you built, whether it is a neutral atom or an ion, and if it is stable. Drag a particle out to remove it.
About the Atom Builder (Isotopes & Ions)
Free atom builder simulation. Add protons, neutrons and electrons, watch the Bohr model shells fill, and see the element, mass number, isotope name and ion charge. Built for atomic & quantum, the atom builder (isotopes & ions) runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Build atoms from protons, neutrons and electrons and see the element, isotope and charge. Use it to explore atomic & quantum ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Atom Builder (Isotopes & Ions)
- Use the controls to change Electron model. The simulation reacts instantly.
- Pick an option such as Shells (rings), Cloud to switch modes or load an example.
- Press "+ Proton", "+ Neutron", "+ Electron", "− Proton" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Build carbon-12, then carbon-14.
- Remove an electron to make a cation.
- Add neutrons and watch the mass number change.
- Make a sodium ion.
Key ideas you can learn
- The number of protons (atomic number) decides which element it is.
- Changing neutrons makes a different isotope of the same element.
- Changing electrons makes an ion: more electrons gives a negative charge, fewer gives positive.
Where this is used in the real world
Understanding protons, neutrons and electrons explains isotopes in carbon dating, ions in batteries and body fluids, and why elements behave differently.
Who is this simulation for?
Advanced high-school and university students in chemistry and physics, and curious learners who want to see how the atomic world behaves.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
What is the difference between an isotope and an ion?
Isotopes have the same protons but different neutrons. Ions have the same protons but a different number of electrons, so they carry a charge.
How do you find the mass number?
Add the protons and neutrons in the nucleus. Electrons are so light they are ignored.
Is the Atom Builder (Isotopes & Ions) free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Atom Builder (Isotopes & Ions) work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.