Explaining the increase in reactivity
2 marks · EasyA potassium atom has 19 electrons. How many electron shells does it have? Show your working.
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4 (±0)
Common mistakes: 3; 5
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Marking points
M1 · 1 mark · Shows or states potassium's configuration: 2,8,8,1 or equivalent working.
A1 · 1 mark · Arrives at 4 (electron shells).
Worked solution
First shell: 2 electrons
Second shell: 8 electrons (total 10)
Third shell: 8 electrons (total 18)
Fourth shell: 1 electron (total 19)
So potassium has 4 electron shells.