Protons (positive particles in the nucleus) were discovered in 1919 by Rutherford.

The mass of a proton is 1.673 X 10⁻²⁴ g.

Neutrons (neutral particles in the nucleus) were discovered in 1932 by James Chadwick.

The mass of a neutron is 1.675 X 10⁻²⁴ g.

	The first experimental evidence of antimater was a particle track observed in a cloud chamber at Caltech by physicist Carl Anderson in 1932. The track curved in the opposite direction of the track of an electron, showing that the particle had a positive charge. This "antielectron" is called the positron.

Today's quantum model, also known as the standard model, explains the structure of atoms using 6 quarks, 6 leptons, and 4 force carriers. According to the standard model, each of the 12 fundamental Fermions has a corresponding antimatter particle.

	A complete list of particles, known and hypothesized, in the Universe.

 

Atomic Theories