Isotopes & Average Atomic Mass Mixer
Mix isotopes of chlorine, copper, boron and more and see the weighted average atomic mass on the periodic table.
Elements are a mixture of isotopes. Choose an element, then change how much of each isotope is in the sample. The average atomic mass is the weighted average, which is the number on the periodic table.
About the Isotopes & Average Atomic Mass Mixer
Free isotopes & average atomic mass mixer. Mix isotopes of chlorine, copper, boron and more and see the weighted average atomic mass on the periodic table. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for atomic & quantum, the isotopes & average atomic mass mixer 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.
Mix isotopes of chlorine, copper, boron and more and see the weighted average atomic mass on the periodic table. 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 Isotopes & Average Atomic Mass Mixer
- Use the controls to change Element, Percent of the lighter isotope. The simulation reacts instantly.
- Pick an option such as Chlorine, Copper, Boron, Lithium to switch modes or load an example.
- Press "Natural mix", "Shuffle sample" 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
- Press Natural mix and compare with the periodic table value.
- Set chlorine to 50 percent of each isotope. How far is the average from the real one?
- Make a boron sample that is nearly all boron-11.
- Find which element has the two closest isotopes in abundance.
Key ideas you can learn
- Isotopes are atoms of the same element with different numbers of neutrons.
- The atomic mass on the periodic table is a weighted average of all the isotopes.
- More of the heavier isotope makes the average heavier.
- A mass spectrum shows each isotope as a bar whose height is its abundance.
Where this is used in the real world
Mass spectrometers use this to identify substances, dating and forensic labs use isotope ratios, and medicine uses isotopes for imaging.
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
Why is atomic mass not a whole number?
Because it is the average over several isotopes, weighted by how common each one is.
What makes an isotope?
The same number of protons but a different number of neutrons.
Is the Isotopes & Average Atomic Mass Mixer 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 Isotopes & Average Atomic Mass Mixer 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.