Isotopes

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.