By 1920, Rutherford had seen evidence for the existence of two subatomic particles and had predicted the existence of a third particle. Protons, electrons, and neutrons are subatomic particles.


Based on experiments with elements other than gold (Au), Rutherford concluded that the amount of positive charge varies among elements. Each nucleus must contain at least one particle with a positive charge. Rutherford called these particles protons. A proton is a positively charged subatomic particle that is found in the nucleus of an atom. Each proton is assigned a charge of 1+. Some nuclei contain more than 100 protons.


The particles that Thompson detected were later named electrons. Electron comes from a Greek word meaning "amber". An electron is a negatively charged subatomic particle that is foud in the space outside of the nucleus. Each electron has a charge of 1-.


In 1932, the English physicist James Chadwick designed an experiment to show that neutrons exist. Chadwick concluded that the particles he produced were neutral because a charged object did not deflect theri paths. A neutron is a neutral subatomic particle that is found in the nucleus of an atom. it has a mass almost exactly equal to that of a proton.

Properties of subatomic particlesEdit

Particle Symbol Relative charge Relative mass (amu) Actual mass (g)
Electron e- 1- 1/1836 9.11 • 10-28
Proton p+ 1+ 1 1.674 • 10-24
Neutron n 0 1 1.674 • 10-24

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