CBSE NOTES CLASS 12 PHYSICS
CHAPTER 13 NUCLEUS
Rutherford proposed that the entire positive charge and nearly the entire mass of atom are concentrated in a very small space called the nucleus of an atom.
The nucleus consists of protons and neutrons. They are called nucleons.
Z - atomic number = number of protons
N - neutron number = number of neutrons
A - mass number = Z + N = total number of protons and neutrons
Nuclear species or nuclides are shown by the notation where X is the chemical symbol of the species. For example, the nucleus of gold is denoted by. It contains 197 nucleons, of which 79 are protons and the rest 118 are neutrons.