Isotopes, Isobars and Isotones

Definition

Three ways of classifying atoms by comparing their numbers of protons (atomic number), mass number (protons plus neutrons), and neutrons.

Key points

• Isotopes are atoms of the same element (same number of protons, same atomic number) with different numbers of neutrons, so they differ in mass number; examples are carbon-12 and carbon-14, or hydrogen, deuterium, and tritium.
• Isobars are atoms of different elements (different atomic numbers) that have the same mass number; an example is argon-40 and calcium-40.
• Isotones are atoms of different elements that have the same number of neutrons.
• Because isotopes have the same number of protons and electrons, they have identical chemical properties but differ in physical properties such as mass; radioactive isotopes (radioisotopes) are used in dating, medicine, and power.
• Uranium-235 and uranium-238 are isotopes used in nuclear technology; carbon-14 is used for radiocarbon dating.

Why it matters for CAPF

The clean distinctions (isotopes same element, isobars same mass number, isotones same neutrons) and stock examples such as carbon isotopes and uranium isotopes are recurring chemistry facts, with links to nuclear technology.

Common confusion

Isotopes share the atomic number (protons) but differ in mass; isobars share the mass number but differ in protons; do not reverse the two. Isotopes of an element behave the same chemically, so they cannot be separated by ordinary chemical reactions, only by physical methods based on mass.

Related concepts

concept radioactivity, concept nuclear fission and fusion, concept acids bases and salts

Parent note

chemistry everyday