The arrangement of the electrons in an atom
3 marks · EasyElement X has atomic number 9. Use this information to answer the following questions.
Write the electronic configuration for atom X.
How many electrons are in the outermost shell of atom X?
Which period is atom X found in?
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) 7
(c) 2
Common mistakes: Incorrect electron splits (e.g., 2,7); Miscounting outer electrons; Confusing period and group
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Marking points
B1 (a) · 1 mark · Gives correct electronic configuration: 2,7.
B1 (b) · 1 mark · Correctly states number of outer electrons: 7.
B1 (c) · 1 mark · States period: 2.
Worked solution
a) With atomic number 9: first shell has 2 electrons, second shell holds up to 8. So, configuration is 2,7.
b) Outermost shell has 7 electrons.
c) There are two shells, so X is in Period 2.