Which one of the following is the correct order of increase of the atomic radius of the elements?
[amp_mcq option1=”C < B < Si < Al" option2="C < B < Al < Si" option3="C < Si < B < Al" option4="Si < Al < C < B" correct="option1"]
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UPSC Geoscientist – 2023
C and B are in Period 2, Group 14 and 13 respectively.
Si and Al are in Period 3, Group 14 and 13 respectively.
Atomic radius generally decreases across a period from left to right due to increasing nuclear charge pulling the electron cloud closer. So, B > C.
Atomic radius generally increases down a group due to the addition of electron shells. So, Si > C and Al > B.
Within Period 3, Al is to the left of Si, so Al > Si.
Comparing elements across periods and groups: Period 3 elements (Si, Al) are generally larger than Period 2 elements (C, B).
Combining these trends:
Within Period 2: C < B Within Period 3: Si < Al Comparing across periods: C and B are smaller than Si and Al. Approximate covalent radii (in picometers, pm): C: 70 pm B: 85 pm Si: 110 pm Al: 125 pm Ordering them in increasing radius: C (70) < B (85) < Si (110) < Al (125). The correct order is C < B < Si < Al.