Electronic configurations and the periodic table
2 marks · EasyPotassium has atomic number 19. Calculate the number of electron shells occupied in a potassium atom.
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4 (±0)
Common mistakes: 3 shells; assuming 19 shells
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Marking points
M1 · 1 mark · Deduces electronic configuration for potassium (2,8,8,1).
A1 · 1 mark · Correctly counts and arrives at 4 shells.
Worked solution
Potassium (atomic number 19):
First shell: 2 electrons
Second shell: 8 electrons (total so far: 10)
Third shell: 8 electrons (total so far: 18)
Fourth shell: 1 electron (total: 19 electrons)
So there are 4 occupied shells.