1. Dalton's Billiard Ball Model (~1803)
John Dalton proposed that matter was composed of tiny, indivisible particles called atoms. He envisioned them as solid, indestructible spheres, much like billiard balls. This first truly scientific atomic theory laid the groundwork for all future discoveries.
- All matter is made of atoms.
- Atoms are indivisible and indestructible.
- Atoms of a given element are identical.
- Chemical reactions are rearrangements of atoms.
Interaction: The solid, uniform sphere represented the atom as a fundamental, unbreakable unit. Drag to rotate the model.
2. Thomson's Plum Pudding Model (~1897)
J.J. Thomson's discovery of the electron shattered the idea of an indivisible atom. He proposed the "plum pudding" model, where negatively-charged electrons were embedded within a uniformly positive sphere.
This was the first model to include subatomic particles, suggesting the atom had an internal structure. The electrons were thought to be somewhat mobile, held in place by the attractive positive charge.
Interaction: Click and drag to rotate. Use the button to see the electrons jiggle, representing their kinetic energy within the atom.
3. Rutherford's Nuclear Model (~1911)
Ernest Rutherford's gold foil experiment revealed that the atom's positive charge and mass were concentrated in a tiny, dense nucleus. His model showed a nucleus composed of protons (and later, neutrons) with electrons orbiting it.
- A dense, positive nucleus contains protons and neutrons.
- Electrons orbit the nucleus like planets.
- The atom is mostly empty space.
Interaction: Rotate and zoom the model. Fire alpha particles to see their paths. Toggle the nucleus view to see its components.
4. Bohr's Planetary Model (~1913)
Niels Bohr refined Rutherford's model by proposing that electrons exist in specific, quantized energy levels or "shells." This explained atomic emission spectra.
- Electrons orbit in shells with fixed energy.
- Electrons can "jump" to higher shells by absorbing energy.
- They emit a photon of a specific color when "falling" to a lower shell.
Interaction: Rotate and zoom. Use the buttons to see an electron jump between energy levels and toggle the level labels.
5. Quantum Mechanical Model (Current)
The modern model treats electrons as waves. We can't know an electron's exact position, only the probability of finding it in a region of space called an orbital. The "electron cloud" is a map of these probabilities.
Orbitals have distinct shapes (s, p, d, f) that describe the probable locations of electrons. This model is the foundation of modern chemistry.
Interaction: Rotate and zoom the electron cloud. Switch between different orbital shapes.