A special kind of nucleus is designated by writing A over Z X. Here X is the chemical symbol of the element, Z is the atomic number (the number of protons in the nucleus), and A is the mass number (the total number of protons and neutrons). Nuclei with the same number of protons but different numbers of neutrons are called isotopes of each other. Nuclei containing certain numbers of protons or neutrons are usually stable. The values of these numbers, are 2, 8, 20, 28, 50, 82, and 126. , they're called the magic numbers,

The properties of a nucleus of an atom include mass, charge, size, shape, spin, and magnetic moment. The positive charge on the proton has exactly the same magnitude as the negative charge on the electron. The mass of a nucleus is around the sum of the free masses of its particles. The attractive nuclear force, nonetheless, causes a small decrease in mass, called the mass defect. The size of a nucleus is possible to be determined by bombarding it with some other particle and measuring its cross-section by the probability of collision. The radius of a nucleus can be find by using the following formula, where A is the mass number.

Neutrons and protons have spins, and their motions within the nucleus may contribute orbital momentum. The orbital momentum plus the spins of the nucleons combine according to the rules of quantum mechanic to give the total spin of the nucleus. The rotation of the electrical charge of the nucleus creates a strong magnetic field. A nucleus is usually approximately spherical in shape, however, some are ellipsoidal.

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