Counting the number of electrons in an atom
2 marks · NormalGive the number of electrons in each of the following neutral atoms:
(a)[1 mark]
Chlorine (atomic number = 17)
(b)[1 mark]
Argon (atomic number = 18)
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(a) 17
(b) 18
Common mistakes: Atomic mass used instead of atomic number
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Marking points
A1 (a) · 1 mark · States that chlorine atom has 17 electrons.
A2 (b) · 1 mark · States that argon atom has 18 electrons.
Worked solution
a) Chlorine: atomic number = 17, so 17 electrons.
b) Argon: atomic number = 18, so 18 electrons.