Electronic configurations and the periodic table
5 marks · HardAn element Y has the atomic number 15.
Write the electronic configuration for element Y.
State the number of electrons in the outer shell of element Y.
Identify the group number and the period number for element Y.
Explain how the electronic configuration relates to the group and period for element Y.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 2, 8, 5
(b) 5
(c) Group 5, Period 3
(d) The number of electrons in the outer shell (5) tells us the group (Group 5). The number of shells (3) tells us the period (Period 3).
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Marking points
A1 (a) · 1 mark · Gives the correct electronic configuration: 2, 8, 5
A2 (b) · 1 mark · States the number of outer shell electrons: 5
A3 (c) · 1 mark · Gives the correct group: Group 5 (accept Group V)
A4 (c) · 1 mark · Gives the correct period: Period 3
B1 (d) · 1 mark · Relates outer shell electrons to group, total shells to period; must reference both group and period clearly.
Worked solution
a) Atomic number 15: 2 electrons in the first shell, 8 in the second, 5 in the third: 2, 8, 5.
b) There are 5 electrons in the outer (third) shell.
c) Number of outer shell electrons = group number = 5 (Group 5). Number of occupied shells = period number = 3 (Period 3).
d) For elements in Groups 1–7, the group number equals the number of electrons in the outermost shell; the period number equals the number of shells with electrons.