Question 1
Multiple choiceEasy1 markA 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?
Show answer and explanation
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.