Physics and Chemistry

Chemical Elements

What is an isotope?

Elements are identified by the number of protons in an atom’s nucleus. Atoms of an element that have different numbers of neutrons are isotopes of the same element. Isotopes of an element have the same atomic number but different mass numbers. Although the physical properties of atoms depend on mass, differences in atomic mass (mass numbers) have very little effect on chemical reactions. Common examples of isotopes are carbon–12 and carbon–14. Carbon–12 has six protons, six electrons, and six neutrons; carbon–14 has six protons, six electrons, and eight neutrons.


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