Pick an element. See its shells.
Every click rebuilds the Bohr model instantly — shells fill from the inside out, and the readout shows exactly how many electrons sit in each ring.
Click, drag, zoom, hover.
The whole model is the interface — no hidden menus.
Pick an element
Choose from the dropdown or tap a tile in the mini periodic grid. The shells rebuild instantly with the correct electron count.
Spin and zoom
Drag anywhere on the stage to rotate the atom in 3D. Use the +/− buttons or scroll wheel to zoom into the nucleus.
Add or remove particles
Use the steppers to turn a neutral atom into an isotope or an ion — the shells and charge badge update live.
Hover any electron
Hover an orbiting electron to see which shell it belongs to. The tooltip tells you exactly where it sits.
What the shells actually show.
Three real facts made visible — not just decoration.
The nucleus
The packed core holds almost all the mass. Protons carry a positive charge; neutrons carry none. Together they set the mass number.
The shells
Each ring is a fixed energy level. Electrons (teal) always fill the innermost open shell first — which is why the model fills from the center outward.
The outer ring
The electrons in the last shell are the ones that bond. The readout highlights this count separately for exactly that reason.
Questions people actually ask.
The short answers — with the long ones one tap away.
What are electron shells?+
Electron shells are fixed energy levels around an atom's nucleus where electrons orbit. The first shell holds up to 2 electrons, the second and third hold up to 8 each in the simple filling order, and the fourth shell continues filling once the third holds its outer 8.
How do electrons fill the shells?+
Electrons always fill the lowest available shell first. Shell 1 fills to 2, then shell 2 fills to 8, then shell 3 fills to 8, then shell 4 begins filling while shell 3 can later expand to 18 for the transition metals.
What are valence electrons?+
Valence electrons are the electrons in the outermost shell. They're the ones involved in chemical bonding, and atoms tend to gain, lose, or share them to reach a full outer shell.
Why does the third shell sometimes hold 8 and sometimes 18?+
For the first 20 elements, shell 3 pauses at 8 while shell 4 begins filling (potassium and calcium). Once you reach the transition metals, shell 3 expands to hold up to 18 electrons — which is why the diagram updates its capacity label automatically.
Is this tool free, and where does my data go?+
It's completely free and runs entirely in your browser — nothing you click or build is uploaded, logged, or sent to any server. No account, no sign-up, no limits.