The atomic nucleus is the central of the atom, with a positive electric charge and in which it is located in most of the mass of the atom. It was discovered by Ernest Ruthenford in 1911. After the discovery of the neutron in 1932, the model of the atomic nucleus was rapidly developed by Dmitri Ivanenko and Werner Heisenberg.
In the nucleus, there is almost all the mass of the atom, with a small contribution from the electron cloud because electrons have less weight compared to neutrons and protons. Protons and neutrons join together to form the atomic nucleus through the nuclear force.
Heisenberg, in 1932, proposed that the nucleus is made up of two types of particles: protons and neutrons (collectively called nucleons). Protons have a positive charge e, equal to and opposite that of the electron, and neutrons are electrically neutral. If Z is the atomic number of an element, there are Z electrons in the shell of its atom and its nucleus has N neutrons, where A = Z + N is the number of nucleons, also called the mass number.
- Atomic number Z. It is the number of protons that make up the nucleus of the atom. Therefore, hydrogen (symbol H), which is the atom used in nuclear fusion, has a number Z = 1, since it only has one proton in its nucleus. The simplest chemical element, and at the same time most abundant in nature is hydrogen.
- Atomic mass A. It is the sum of protons and neutrons. It is also called a mass number. Considering N: the number of neutrons in an atom, we have:
A = Z + N.
- Atomic weight. It is the weight of the atom, to calculate it we must take as a unit the twelfth part of the weight of the carbon atom (C). Therefore, hydrogen weighs about 1 and carbon 12.
- Isotope. The same type of atom can have a different number of neutrons in its nucleus. Each variety is called an isotope. Therefore, hydrogen has three different isotopes: hydrogen isotope, deuterium isotope, and tritium isotope. These last two are those used in nuclear fusion.
The scientific branch that is responsible for the study and understanding of the atomic nucleus, including the forces that unite it and its composition is nuclear physics.
