Relative atomic mass
2 marks · EasyA sample contains atoms of oxygen-16 () and oxygen-18 (). Both are isotopes of oxygen.
State the number of protons and the number of neutrons in an atom of .
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Number of protons = 8, number of neutrons = 10
Also accept: Protons: 8, Neutrons: 10; 8 protons and 10 neutrons; Number of neutrons = 10, number of protons = 8
Common mistakes: Swapping protons and neutrons; Using 16 as mass number for both isotopes
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Marking points
M1 · 1 mark · Correctly identifies that oxygen always has 8 protons (atomic number = 8).
A1 · 1 mark · Correctly calculates number of neutrons in as 10.
Worked solution
The atomic number of oxygen is 8, so has 8 protons.
Number of neutrons = mass number - atomic number
So an atom of has 8 protons and 10 neutrons.