About this experiment
Build an atom by changing its protons, neutrons and electrons. Use a rotating counting diagram to connect nuclear charge, isotope mass number, ionic charge and shell populations.
Learning goals
- Distinguish the roles of protons, neutrons and electrons.
- Construct neutral atoms and ions and calculate their charges.
- Connect shell populations with a simple ground-state subshell configuration.
How to use it
- 1Start with carbon-12 and inspect its two occupied shells.
- 2Add one neutron and compare the mass number with the unchanged electron configuration.
- 3Add a proton while keeping the atom neutral and identify the new element.
- 4Turn off neutral mode and remove one electron; record the charge and shell populations.
The model
Assumptions
- Only 1s, 2s, 2p, 3s, 3p and 4s are filled, in that order, for at most 20 electrons.
- Moving dots on shell rings are a counting aid, not classical electron orbits or quantum probability densities. Nuclear and electronic lengths use independent visual scales.
- Nuclear stability, binding energies and whether an arbitrary negative ion is bound are outside this model. Mass number is not a measured atomic mass.
Try this in class
- Q1Why does adding a neutron change the isotope but not the element?
- Q2What remains unchanged when a neutral atom loses an electron?
Frequently asked questions
Are electrons really tiny planets on these circles?
No. Quantum states do not assign those paths. The animation helps count shell populations only.
Does every nucleus built here exist as a stable isotope?
No. Proton and neutron counts can be varied as a bookkeeping exercise. Stability and radioactive decay are not inferred.