Thomson → Rutherford → Bohr → Schrödinger Eₙ = -13.6 Z²/n² eV
Thomson (1897)
Rutherford (1911)
Bohr (1913)
Quantum (1926)
Presets · choose a demonstration Thomson — Plum Pudding
Positive sphere with embedded electrons.
Rutherford — Gold Foil
α-particles scatter off a dense nucleus.
Bohr — Ground State
n=1 at the Bohr radius a₀ = 0.529 Å.
Bohr — Lyman Series
Cycle between n=1 and higher levels through n=7.
Bohr — Balmer Series
Cycle between n=2 and higher levels through n=7.
Bohr — Paschen Series
Cycle between n=3 and higher levels through n=7.
Bohr — Brackett Series
Cycle between n=4 and higher levels through n=7.
Bohr — Pfund Series
Cycle between n=5 and higher levels through n=7.
Bohr — Humphreys Series
Cycle between n=6 and higher levels through n=7.
Bohr — Fine Structure
Spin-orbit coupling splits j = l ± ½.
Bohr — Zeeman Effect
Magnetic field splits degenerate levels.
Quantum — 1s Orbital
Spherically symmetric ground state.
Quantum — 2p Orbital
Dumbbell shape with one angular node.
Quantum — 3d Orbital
Cloverleaf with two angular nodes.
Quantum — 4f Orbital
Complex multi-lobed f-orbital.
Simulation ⛶ Expand simulation
Thomson · plum-pudding atom The pink pudding is a continuous sphere of positive charge. Blue negative electrons are the embedded plums. The + symbols mark the positive medium, not separate protons; this model has no nucleus.
Pink pudding: distributed positive charge · Blue plums: negative electrons
Diagram sizes are schematic. Zoom magnifies the view; drag to pan and use Fit to restore framing.
More parameters ▼
Calculated
Electrons 1
Protons 1
Net charge 0 e
Curriculum
WAEC NECO IGCSE SAT JUPEB A-Level
Teacher notes · Thomson: charge spread through the atom Learning goal: Explain the plum-pudding picture and distinguish electrical neutrality from an absence of charge.
The shaded positive sphere represents positive charge distributed throughout the atom. The embedded negative electrons are the plums. This model contains no compact central positive nucleus; the sphere is not an electron orbit.
For a neutral atom, total positive charge +Ze balances electron charge −Ne when Ne=Z. A neutral object can contain many charges. Removing an electron leaves a positive ion without changing the positive charge.
The electron animation is illustrative motion inside the proposed positive material. It is not measured electron trajectories or evidence that the model correctly predicts atomic spectra.
Ask learners what a spread-out positive charge would imply for an energetic positive probe. Contrast gentle cumulative deflection with the rare large-angle events that challenged this picture. Thomson’s model cannot account for those events with a tiny dense scattering centre.
Demonstration and discussion Identify the positive background and negative electrons. Pause and sketch the charge distribution. Switch to Rutherford and ask what evidence requires the positive charge to be concentrated instead.
Worked example If Z=6 and Ne=5, Q=(Z−Ne)e=+e=+1.602×10⁻¹⁹ C. One electron must be added for neutrality; adding a neutron would not restore it.
Student investigation · 4 activities Predict first, record your settings and observations, then explain using the model. Submit a labelled sketch, calculations with units, and one limitation.
Draw and annotate the model. Where are the two signs of charge, and where is its nucleus?
Check your reasoning Positive charge fills the sphere; negative electrons are embedded. There is no compact nucleus in this model.
A proposed atom has +8e and ten electrons. Find its net charge and explain the sign.
Check your reasoning Q=(8−10)e=−2e=−3.204×10⁻¹⁹ C. Two excess electrons give a negative ion.
Predict whether a diffuse positive sphere or a concentrated nucleus better explains an alpha particle returning towards its source. Explain.
Check your reasoning A concentrated positive nucleus produces a strong repulsive force in a close approach; diffuse charge cannot explain the observed rare large deflections in the same way.
Write a claim, evidence and limitation paragraph comparing this model with Rutherford.
Check your reasoning Claim: atomic charge is separated. Evidence: electrons exist. Limitation: diffuse positive charge fails to explain large-angle scattering; Rutherford concentrates positive charge in the nucleus.
Further reading: OpenStax: Bohr model and spectra · Hydrogen atom and quantum states . Split-level drawings and orbital slices are teaching approximations.
