Glossary term: Nucleon
Description: All the matter that we see around us is made up of atoms, and all atoms have the same basic structure: a tiny, dense nucleus that carries almost all of the atom's mass, surrounded by electrons. The main constituents of atomic nuclei are protons and neutrons, which are collectively called nucleons.
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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher
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Related Diagrams
Nucleon
Caption: A nucleon is a constituent of an atomic nucleus. For normal matter, nucleons can be either protons or neutrons. The number of nucleons defines the mass number of a nucleus while the number of protons defines the atomic number. Atomic nuclei of a particular chemical element all have the same atomic number but can have different mass numbers. Nuclei with the same atomic number but different mass numbers are known as isotopes. Most elements have more than one isotope that occurs in nature although a few only have one isotope that is stable over long periods of time.
This diagram shows the nuclei of isotopes of the first six chemical elements (from left to right: hydrogen, helium, lithium, beryllium, boron and carbon). Beside each chemical element symbol are two numbers. The upper number is the mass number, the number of nucleons. The lower number for each is the atomic number, the number of protons.
Credit: Maria Cristina Fortuna/IAU OAE
License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
