Isotope

An isotope is one of two or more atoms of the same chemical element with different numbers of neutrons. Isotopes share an atomic number but have different mass numbers.

Atomic number: The number of protons in an atom’s nucleus, which determines its chemical element. Isotopes of one element all have the same atomic number.
Nuclear stability: The tendency of an atomic nucleus to remain intact rather than undergo spontaneous change. The balance of protons and neutrons governs an isotope’s stability.
Radiometric dating: A method of determining age by measuring radioactive decay in a material. Known decay rates turn radioactive isotope ratios into age estimates.
Carbon-12: A stable carbon isotope with six protons and six neutrons. It is the reference isotope that defines the atomic mass unit.
Ion: An atom or molecule with a net electric charge from gaining or losing electrons. Ionization changes electron count, whereas isotopic variation changes neutron count.
Mass number: The total number of protons and neutrons in an atom’s nucleus. Different neutron counts give isotopes of an element different mass numbers.
Radioactive decay: The spontaneous transformation of an unstable atomic nucleus, often with emitted particles or radiation. Unstable isotopes change into other nuclides through radioactive decay.
Carbon-14 dating: A method for dating once-living materials by measuring their carbon-14 content. Carbon-14 is a radioactive isotope used to date archaeological and geological samples.
Carbon-14: A radioactive carbon isotope with six protons and eight neutrons. Its decay underpins a widely used method for dating once-living material.
Isobar: A nuclide with the same mass number as another nuclide but a different atomic number. Isobars share mass number, unlike isotopes of one element, which share atomic number.

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