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GCSE Physics · key term
An atom of an element that has the same number of protons as other atoms of that element but a different number of neutrons.
Used by Edexcel
Specification 6.3, 6.25 · Paper 1
Revise: Isotope StructureIsotopes are atoms of the same element whose nuclei contain the same number of protons but different numbers of neutrons.
An atom of an element with a particular number of neutrons in its nucleus.
When deciding whether two atoms are isotopes, compare their atomic numbers first: isotopes must have the same but different .
Mass number is a whole number for one particular isotope. Do not confuse it with the relative atomic mass shown as a decimal on many periodic tables.
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