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In 1932 James Chadwick found the missing piece — a particle with the mass of a proton but no charge at all.
- A subatomic particle with no electric charge (neutral).
- Its mass is nearly equal to that of a proton.
- Found in the nucleus of all atoms except hydrogen ; symbol n .
| S.No. | Subatomic particle | Symbol | Relative charge |
|---|---|---|---|
| 1 | Electron | e − | −1 |
| 2 | Proton | p + | +1 |
| 3 | Neutron | n 0 | 0 |
Lighter atoms often have equal protons and neutrons (carbon: 6 each; oxygen: 8 each). Heavier atoms need more neutrons than protons (iron: 26 p, 30 n; uranium: 92 p, 146 n). Protons repel one another because they are all positive; neutrons help by spacing protons apart and by strengthening the nuclear force that binds the nucleus together.
The discovery of the neutron opened a new era in atomic physics. Being uncharged, neutrons can easily enter nuclei, leading to artificial radioactive elements and the splitting of uranium — giving birth to the ‘atomic age’ of nuclear power and nuclear weapons.
- Worked under Rutherford at the Cavendish Laboratory, Cambridge.
- Discovered the neutron in 1932 , explaining atomic mass.
- Won the Nobel Prize in Physics (1935) .
The Bhabha Atomic Research Centre (BARC) , Mumbai, leads advanced neutron-scattering experiments using reactors such as Dhruva . This reveals insights into superconductors, battery electrodes and drug molecules — helping develop better medicines, energy storage and industrial alloys in India.
- Neutron — a neutral subatomic particle (no charge) in the nucleus, with mass nearly equal to a proton.
- Nuclear force — the strong force that binds protons and neutrons together in the nucleus.
| Particle | Symbol | Relative charge | Location |
|---|---|---|---|
| Electron | e − | −1 | Outside the nucleus (in shells) |
| Proton | p + | +1 | Inside the nucleus |
| Neutron | n 0 | 0 | Inside the nucleus |
