3.8.1.1
The nuclear model replaced the plum pudding model through experimental evidence
Nuclear Structure & Radiation — AQA A-Level Physics
- Dalton (1803): atoms are solid, indivisible particles. Atoms of one element are identical; different elements have different atoms.
- Thomson (1897): discovered the electron. Proposed the 'plum pudding' model — a sphere of uniform positive chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). with electrons embedded throughout.
- Rutherford (1909-1911): alpha scattering disproved the plum pudding model. Most particles passed through, but some were deflected or back-scattered. Concluded: small, dense, positive nucleus surrounded by electrons.
- Bohr (1913): electrons orbit the nucleus in well-defined shells at specific energyThe capacity to do work. Measured in joules (J). levels.
- Chadwick (1932): discovered the neutron, completing the model of the atom as protons + neutrons in the nucleus, electrons in shells.
Common Mistake
MEDIUM
Students often: Don't say Rutherford discovered the nucleus by firing electrons at gold foil.
Instead: Rutherford used alpha particles, not electrons. Alpha particles are positively charged helium nuclei — their repulsion from the nucleus is what revealed its existence.
Instead: Rutherford used alpha particles, not electrons. Alpha particles are positively charged helium nuclei — their repulsion from the nucleus is what revealed its existence.