Question

In each of the following sets, which atom or ion has the smallest radius?

1. H, He
2. Cl, In, Se
3. Element 120, element 119, element 117
4. Nb, Zn, Si
5. $\mathit{N}{\mathit{a}}^{\mathbf{-}}$,Na,${\mathbf{Na}}^{\mathbf{+}}$

Short answer

1. He
2. Cl
3. Element 117
4. Si
5. ${\mathrm{Na}}^{+}$
   

Step-by-step solution

Describe the trends of atomic radii in the periodic table.

We know that atomic radius decreases along the period and increases down the group.

Determine the positions of elements in the periodic table to predict their size.

1. H(1) = 1s’ and He(2) =$1{\mathrm{s}}^2$

On moving left to right in a period, the radius decreases because the effective nuclear charge increases.

So, He will have the smallest radius.

1. Cl(17) = Group 17 and period 3.

In(49) = Group 13 and period 5.

Se(34) = Group 16 and period 4.

Elements belonging to period 3 will be smaller than those belonging to period 4, which, in turn, will be smaller than those belonging to period 5.

So, Cl will have the smallest radius.

1. Element 120 = Group 2 and period 8.

Element 117 = Group 17 and period 7.

Element 120 = Group 1 and period 8.
Elements belonging to period 7 will be smaller than period 8 elements.

So, element 117 will be the smallest among these.

1. Nb(41) = group 5 and period 5.

Zn(30) = group 12 and period 4.

Si(14) = group 14 and period 3.

Elements belonging to period 3 will have a smaller size than period 4 and 5 elements.

So, element Si will have the smallest radius.

Find the trend of radius in ions.

We know that cation is smaller than the parent atom whereas anion is larger than the parent atom. elements.

So, will have the smallest radius.