Electronic configurations and the periodic table
2 marks · HardExplain why an atom with the electronic configuration 2, 7 is placed in both Group 7 and Period 2 of the Periodic Table.
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There are 7 electrons in the outer shell, so it is in Group 7; there are 2 shells so it is in Period 2.
Also accept: It has two electron shells so is in period 2; seven electrons in its outer shell so is in Group 7.; Group 7 because of 7 outer electrons; Period 2 because it has 2 shells
Common mistakes: Confusing total electrons with period; Using total electrons for group number
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Marking points
M1 · 1 mark · Links 7 outer shell electrons to group 7
M2 · 1 mark · Links 2 occupied shells to period 2
Worked solution
Number of outer shell electrons = 7, so the atom is in Group 7. Number of shells filled = 2, so the atom is in Period 2.