Counting the number of electrons in an atom
2 marks · EasyCalcium has an atomic number of 20. Calculate the number of electrons in a neutral atom of calcium. Show your working.
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Show answer
20
Must show: Working shows number of electrons equals atomic number
Common mistakes: Confusing atomic mass and atomic number
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Marking points
M1 · 1 mark · States or uses the rule that in a neutral atom, number of electrons = atomic number.
A1 · 1 mark · Gives the correct answer: 20 electrons.
Worked solution
In a neutral atom, number of electrons = atomic number.
Therefore, a neutral atom of calcium has 20 electrons.