IB Chemistry HL S3.1 The periodic table: classification of elements questions

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Question 1

Multiple choiceEasy1 mark

A data set gives atomic radii for four consecutive period 3 elements: Na, 186 pm; Mg, 160 pm; Al, 143 pm; Si, 118 pm. What is the mean decrease in atomic radius per step from Na to Si, to the nearest whole picometre?

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Answer: B. The mean decrease per step is the total decrease divided by the number of intervals: (186 − 118) pm ÷ 3 = 22.7 pm, which rounds to 23 pm.

A: divides the total decrease by the four elements rather than the three intervals, giving 17 pm. C: divides by two instead of three intervals, giving 34 pm. D: gives the total decrease, 68 pm, rather than the mean decrease per step.

Remember: four consecutive elements have three intervals between them.

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