Developing models of atoms
Niels Bohr adapted Ernest Rutherford's nuclear model. Bohr did calculations that led him to suggest that electrons orbit the nucleus in shells. The shells are at certain distances from the nucleus. The calculations agreed with observations from experiments.
Further experiments led to the idea that the nucleus contained small particles, called Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1.. Each proton has a small amount of positive charge.
In 1932 James Chadwick found evidence for the existence of particles in the nucleus with mass but no charge. These particles are called Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0.. This led to another development of the atomic model, which is still used today.