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Isotopes

Isotopes of an element have the same number of protons, but different numbers of neutrons in their nuclei. Isotopes of an element have:

• the same atomic number
• different mass numbers

Three isotopes of hydrogen

All hydrogen atoms contain one proton (and one electron), but they can contain different numbers of neutrons. Hydrogen-1 is the most abundant isotope of hydrogen.

All three isotopes of hydrogen have identical chemical properties. This is because the number of electrons determines chemical properties, and the atoms of all three isotopes have one electron.

Learn more on isotopes in this podcast.

Listen to the full series on 91�ȱ� Sounds.

Ions

Ions are charged particles formed when atoms, or groups of atoms, lose or gain electrons:

• positively charged ions form when electrons are lost
• negatively charged ions form when electrons are gained

The charge on an ion is shown as a superscript. For example, an aluminium ion Al³⁺ carries 3 positive charges. It forms when an aluminium atom loses 3 electrons.

When you calculate the number of subatomic particles in an ion, you need to take into account the number of electrons lost or gained.