Atom Builder
Everything is made of atoms, and every atom is just three kinds of particle. Add protons to pick the element, neutrons to change the isotope, and electrons to make an ion — and watch a live Bohr atom rearrange its shells around you.
The three particles, and what each one decides
- Protons — the count of protons is the element. One proton is always hydrogen; six is always carbon. Change the protons and you change what substance you have.
- Neutrons — add mass without changing the element. Same protons + different neutrons = an isotope. Carbon-12 and carbon-14 are both carbon; one is used to date ancient bones.
- Electrons — balance the charge. Equal to the protons → a neutral atom. Fewer → a positive ion (cation). More → a negative ion (anion).
How to read the symbol
Chemists write an atom as its symbol with two small numbers on the left — the mass number (protons + neutrons) on top and the atomic number (protons) on the bottom — and the charge on the right:
Try building oxygen (8 protons, 8 electrons), then add 2 more electrons to make the O²⁻ ion you'll meet in water and rust. Watch the outer shell click shut at 8 — that "full shell" is exactly why oxygen grabs electrons so hungrily.
Things worth trying
- Build neon (10) and argon (18): both fill their outer shell perfectly. That's why the noble gases barely react.
- Build sodium (11), then remove one electron. It drops to the neon shell pattern (2·8) and becomes Na⁺ — the sodium in table salt.
- Keep the protons on carbon (6) and just add neutrons: 6 → 7 → 8. You're stepping through carbon-12, -13, and radioactive carbon-14 without changing the element at all.