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If you look at the pictures you will see that there are two 'versions' of hydrogen. One of them has a nucleus containing a proton but the other has a nucleus with both a proton and a neutron. These two 'versions' of hydrogen are called ISOTOPES of hydrogen.

Isotopes are nuclei with the same number of protons (proton number) but with a different number of neutrons. This means that they will have a different mass number (nucleon number).

Almost all elements have naturally occurring isotopes and many more can be made in the laboratory.

Basically, isotopes of an element are all the same element (they have the same number of protons) but they have different masses. The chemical properties of all the isotopes of an element will be the same but their physical properties will be different because of their different masses. This means that properties like the boiling point and density of isotopes of an element will be different. For example 'heavy water' containing the isotope of hydrogen 21H (called deuterium) has a boiling point of 104 oC. Radioactive isotopes (with different half lives) are used for a variety of purposes see the section on half-life.

A few isotopes of some of the elements are shown in the table below.

Element Proton number Neutron number Nucleon number
Hydrogen 1 0 1
Deuterium 1 1 2
Tritium 1 2 3
Carbon 6 6 12
Carbon 6 8 14
Oxygen 8 8 16
Oxygen 8 10 18
Neon 10 10 20
Neon 10 11 21
Neon 10 12 22
Cobalt 27 32 59
Cobalt 27 33 60
Uranium 92 143 235
Uranium 92 146 238

Carbon 14 (6 protons and 8 neutrons) and carbon 12 (6 protons and 6 neutrons) are two isotopes of carbon.

Radioactive isotopes (radio isotopes) are ones that are radioactive and emit either alpha, beta or gamma radiation. These are used for a variety of purposes in medicine and industry.


© Keith Gibbs 2020