The History of the Atomic Model: Chadwick and the Neutron


By the 1930’s the atom consisted of a proton as a positive area of charge and electrons orbiting it but there was still a piece missing. It was not until 1932 that James Chadwick discovered a particle with the same mass of a proton but no overall charge, the neutron.

The Atom until 1930 consisted of a positive particle in the centre with most of the mass and then some negatively charged electrons orbiting around it in different energy levels. In 1920 chemical isotopes were discovered and atomic masses determined for a number of elements this stretched the current theory of there just being protons and electrons in the atom and in 1932 James Chadwick discovered the neutron. James Chadwick created radiation from a radioactive Beryllium isotope and aimed this at Paraffin wax, a large hydrocarbon. Chadwick then measured the range of the protons that were given off and he found that instead of gamma waves being produced that a particle of the same mass as a proton but uncharged had been produced. Chadwick’s discovery of the neutron led to the discovery of radioactivity and nuclear fission which lead to the creation of nuclear power and the first atomic bomb.

Terms in section

Isotopes are atoms of the same element with different number of neutrons and the same number of protons. React chemically the same but have a different masses

James Chadwick

James Chadwick was a British physicist who worked with Beryllium isotopes and alpha particles to produce neutral electrical charges which he termed a neutron.


A neutron is a neutral sub atomic particle that makes up the nucleus with the proton


A hydrocarbon is the term given to a compound composed of just hydrogen and carbon.


Gamma particles that are made of waves released from a nucleus when it breaks apart


Radioactivity is a property of some elements where the nucleus breaks down and turns into smaller parts to release energy

Nuclear Fission

Nuclear fission is the process of splitting up large atoms to release heat energy to be used in the generation of electricity


The History of the Atomic Model: Wave Particle Duality


The History of the Atomic Model: Rutherford and Bohr