Question

Explain the trends in the following properties of group 17 elements : Atomic radii

Hint:

Down the group: Number of shells increases $\rightarrow$ Shielding effect increases $\rightarrow$ Effective nuclear charge decreases $\rightarrow$ Atomic size increases.

Answer 1

Step 1: Understanding the Concept:
Atomic radius is the distance from the center of the nucleus to the outermost shell containing electrons.
Step 2: Detailed Explanation:
In Group 17 (Halogens), as we move down the group from $F$ to $Cl, Br, I$, and $At$:
1. A new principal energy level (shell) is added at each successive element.
2. Although the nuclear charge increases, the effect of adding a new shell is more dominant.
3. The increased distance of the outermost electrons from the nucleus and the shielding effect of inner electrons result in an increase in the size of the atom.
Order: \( F<Cl<Br<I<At \).
Step 3: Final Answer:
The atomic radii increase down the group due to the addition of new electronic shells.