Question

Which of the following is a correct order of atomic sizes: $\mathrm{Ce}\left(58\right)$, $\mathrm{Sn}\left(50\right)$, $\mathrm{Yb}\left(70\right)$, and $\mathrm{Lu}\left(71\right)$?

• A. $\mathrm{Sn}>\mathrm{Lu}>\mathrm{Yb}>\mathrm{Ce}$
• B. $\mathrm{Ce}>\mathrm{Yb}>\mathrm{Sn}>\mathrm{Lu}$
• C. $\mathrm{Ce}>\mathrm{Sn}>\mathrm{Yb}>\mathrm{Lu}$
• D. $\mathrm{Lu}>\mathrm{Ce}>\mathrm{Sn}>\mathrm{Yb}$

Answer 1

The correct option is C

$\mathrm{Ce}>\mathrm{Sn}>\mathrm{Yb}>\mathrm{Lu}$

Explanation for the correct option:

C. $\mathrm{Ce}>\mathrm{Sn}>\mathrm{Yb}>\mathrm{Lu}$

Trend of atomic size in periodic table:

• On moving from left to right in a periodic table, the atomic radius of an atom decreases due to the addition of an extra proton which leads to a stronger pull of electrons while the extra electron goes to the same principal energy level.
• While going down in a group, an extra energy level adds to the structure which leads to an increase in atomic radius. Thus, on moving down the group, the atomic radius increases.
• Cerium ($\mathrm{Ce}$) belongs to Lanthanoids, Tin ($\mathrm{Sn}$) belongs to Group 16 and period 4, Ytterbium ($\mathrm{Yb}$), and Lutetium ($\mathrm{Lu}$) also belong to lanthanoids.
• Lanthanoids are considered in the sixth period.
• There is a sharp decrease in the atomic size of lanthanoids from $\mathrm{Ce}>\mathrm{Yb}>\mathrm{Lu}$ as a result of lanthanoid contraction. The size of $\mathrm{Yb}$ and $\mathrm{Lu}$ is smaller than $\mathrm{Sn}$.
• Thus, the correct order of atomic size is $\mathrm{Ce}>\mathrm{Sn}>\mathrm{Yb}>\mathrm{Lu}$.

Explanation of incorrect options:

The correct order of atomic size is $\mathrm{Ce}>\mathrm{Sn}>\mathrm{Yb}>\mathrm{Lu}$. Thus, options A, B, and D are incorrect.

Hence, the correct option is C i.e. $\mathrm{Ce}>\mathrm{Sn}>\mathrm{Yb}>\mathrm{Lu}$