Counting the number of electrons in an atom
3 marks · NormalCalculate the number of electrons in a sample containing 5 neutral atoms of beryllium. Atomic number of beryllium = 4. Show your working.
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Show answer
20
Also accept: 4 × 5 = 20
Common mistakes: Multiplying incorrectly
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Marking points
M1 · 1 mark · States or uses number of electrons in one beryllium atom (4).
M1 · 1 mark · Multiplies by 5 to find total electrons for 5 atoms.
A1 · 1 mark · Gives final answer of 20 electrons. (follow-through)
Worked solution
Each neutral atom of beryllium has the same number of electrons as its atomic number, which is 4.
Number of electrons in 5 atoms = 4 × 5 = 20 electrons.