The Periodic Table
5 marks · EasyThis question is about working out and interpreting electronic configurations.
An atom has 9 electrons. Write its electronic configuration using numbers and commas.
Below is a diagram showing the electronic configuration of an atom:
There are 2 crosses in the inner shell and 7 crosses in the second shell.
Explain which element this atom is by giving its name and how you worked it out.
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) 2,7
(b) 2 in first shell, 7 in second shell; so configuration is 2,7
(c) The element is fluorine (atomic number 9), since the atom has 9 electrons (2+7). Element with atomic number 9 is fluorine.
Common mistakes: Incorrect electron filling order; confusion between number of electrons and protons
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Marking points
B1 (a) · 1 mark · Correctly writes 2,7 for electronic configuration of 9 electrons.
B2 (b) · 1 mark · Correctly identifies 2 electrons in first shell, 7 in second shell.
B3 (b) · 1 mark · States arrangement as 2,7 or states number of electrons in each shell explicitly.
B4 (c) · 1 mark · Correctly states that the atom has 9 electrons/atomic number 9.
B5 (c) · 1 mark · Names the element as fluorine.
Worked solution
a) For 9 electrons: 2 fill first shell, 7 fill second. Configuration is 2,7.
b) Diagram shows 2 in first shell, 7 in second shell, so electronic configuration is 2,7.
c) The element with atomic number 9 (because neutral atoms have electrons = atomic number) is fluorine.