The arrangement of the electrons in an atom
5 marks · HardElement Y has an atomic number of 17.
Write the full electronic configuration of element Y.
How many electron shells does an atom of element Y have?
In which group of the Periodic Table is element Y found? Explain your answer.
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(a) 2,8,7 · must show Correct sequence: 2 in first, 8 in second, 7 in third shell.
(b) 3 · must show Recognises 3 shells.
(c) Group 7. It is because there are 7 electrons in the outer shell. · must show States Group 7; links to 7 outer electrons.
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Marking points
M1 (a) · 1 mark · Correct method to fill shells, up to third shell (first: 2, second: 8, third: 7).
A1 (a) · 1 mark · Full correct configuration: 2,8,7 (in correct order).
B1 (b) · 1 mark · States 3 shells/energy levels for element Y. (follow-through)
B2 (c) · 1 mark · States group number as Group 7. (follow-through)
B3 (c) · 1 mark · Links group to 7 electrons in outer shell (explanation).
Worked solution
a)
So, the configuration is 2,8,7.
b)
There are three shells (energy levels).
c)
Element Y is in Group 7 because it has 7 electrons in its outer shell.