Electronic configurations and the periodic table
2 marks · NormalState the number of electron shells and the number of electrons in the outer shell for an atom of phosphorus (atomic number 15).
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Phosphorus has 3 electron shells (period 3) and 5 electrons in its outer shell (group 5).
Also accept: 3 shells, 5 outer electrons; Three shells; five electrons in outer shell
Common mistakes: Stating 2 shells; Stating 8 or 0 outer electrons
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Marking points
B1 · 1 mark · States correct number of electron shells (3)
B2 · 1 mark · States correct number of outer electrons (5)
Worked solution
Phosphorus has atomic number 15, so electronic configuration is 2,8,5.
It has 3 shells (since there are 3 numbers in the configuration; period 3).
There are 5 electrons in its outer shell (last number).