This simulator builds an atom or ion from three counts: protons, neutrons and electrons. The proton count fixes the element, protons plus neutrons give the mass number, and the electron count relative to protons sets the net charge. A sampled cloud of dots shows electron occupancy in shells.
• A nucleus of protons and neutrons, an electron occupancy cloud, shell occupancy guides and a charge balance scale. • Three count sliders: protons or atomic number (1 to 18), neutrons (0 to 22) and electrons (0 to 18), plus a toggle for explanatory particles. • Readouts: atomic number, mass number, net charge in units of e, electron count and outer occupied shell electrons. • Experiments: Carbon-14 (Z = 6, 8 neutrons, mass number 14, neutral) and a sodium ion (Z = 11, 12 neutrons, 10 electrons, net charge +1 e).
Mass number A = Z + N, and net charge in units of e is Z − N_electrons. The first 18 electrons fill in the order 1s², 2s², 2p⁶, 3s², 3p⁶, so the outer occupied shell readout shows how many electrons sit in the last partly or fully filled shell.
Counts are exact but the geometry is illustrative, not a multi-electron wavefunction. The cloud is a sample of occupancy, not electron orbits. Arbitrary isotope and ion choices are allowed and are not claims of stability. Nuclear and electronic dimensions are not to scale.
The number of protons. Changing the proton count changes the element, while changing neutrons gives a different isotope and changing electrons gives an ion.
No. They illustrate occupancy, not trajectories. Electrons do not follow planetary paths, and the cloud only shows how many occupy each shell.
Remove electrons while keeping the proton count. The Sodium ion experiment sets 11 protons and 10 electrons, giving a net charge of +1 e.
No. You can choose any neutron count, but that is not a claim the nucleus is stable. The lab only tracks counts, mass number and charge.