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How do isotopes occupy the same position in the periodic table?

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Periodic table of the elements with color-coded categories and labeled element groups, showing atomic numbers, symbols, and basic information for each chemical element. — periodic table Modern version of the periodic table of the elements. To learn an element's name, atomic number, electron configuration, atomic weight, and more, select one from the table.

Isotopes occupy the same position in the periodic table because they share the same atomic number, which is the number of protons in the nucleus of an atom.12

The periodic table is organized based on the atomic number, which determines an element's identity and its chemical behavior. Because isotopes of a given element have the same number of protons—and consequently the same number of electrons in a neutral atom—they exhibit nearly identical chemical properties.321

The variation between isotopes arises solely from differences in the number of neutrons in their nuclei, which results in different atomic masses and physical properties. Since the periodic table is structured by the atomic number rather than mass, all isotopes of a specific element are grouped together in the single place assigned to that element.124