A new isotope has 20 protons, 22 neutrons, and 20 electrons. How does its mass number affect its chemical behavior compared to other isotopes of the same element?
The mass number does not affect chemical behavior because chemical properties depend mainly on the number of electrons.
Isotopes are atoms of the same element with the same atomic number (number of protons) but different numbers of neutrons, and therefore different mass numbers. Here, 20 protons means the element is calcium, and its mass number is 20 + 22 = 42.
Chemical properties depend on the number of electrons, especially the valence electrons, and their arrangement. All isotopes of an element have the same number of electrons (20 here) and the same electronic configuration (2, 8, 8, 2 for calcium), so their chemical behavior is essentially the same.
Extra neutrons change only the mass and nuclear properties. They do not change the electron arrangement, do not decide the number of electrons (which equals the number of protons in a neutral atom), and do not make an isotope always more reactive.
Hence, The mass number does not affect chemical behavior because chemical properties depend mainly on the number of electrons.
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