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Glossary term: Isótopo

Description: Os núcleos atômicos são formados por nêutrons e prótons. O número de prótons em um núcleo é o chamado “número atômico”, que determina o elemento químico correspondente: átomos com um único próton são átomos de hidrogênio, aqueles com seis prótons são de carbono, e assim por diante. Núcleos atômicos que têm o mesmo número de prótons, mas diferentes números de nêutrons, são chamados de isótopos do elemento químico em questão. Os núcleos de hidrogênio comuns possuem apenas um único próton e nenhum nêutron. Um núcleo com um próton e um nêutron ainda é hidrogênio, mas “hidrogênio pesado”, também chamado de deutério. Em geral, apenas alguns isótopos de um determinado elemento são estáveis. Os outros se decompõem radioativamente em núcleos mais estáveis.

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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition is still awaiting approval

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A diagram with nuclei of isotopes of 6 elements with sketches of the nucleus accompanied by the chemical element symbol & the mass & atomic numbers

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

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