Isotopes

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Isotopes are atoms that have the same number of protons but a different number of neutrons.

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Three isotopes of hydrogen would all have the same number of protons and electrons but would have a different number of neutrons. These isotopes could have:

• 1 proton, 1 electron and 1 neutron 

• 1 proton, 1 electron and 2 neutrons

• 1 proton, 1 electron and 3 neutrons 

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We name isotopes after their element name and their mass number. For example, chlorine-37 is an isotope of chlorine that has a mass number of 37.