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AQA · GCSE · Physics · Higher

Neutrons from Isotope Notation

Q02.2 1 mark

A gold atom has the symbol:

79197Au{}^{197}_{79}\mathrm{Au}

How many neutrons are there in this gold atom?

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Marking points

  1. 1 Gives 118 neutrons.

Full-mark answer

Number of neutrons = mass number − atomic number = 197 − 79 = 118.

Why this answer loses marks

Uses the atomic number as the neutron count.

Atomic number counts protons; subtract it from the mass number to find neutrons.

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