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:
The atomic radius is the distance from the center of the nucleus to the outermost shell of an atom. In a group, this is primarily influenced by the number of energy levels.
Step 3: Detailed Explanation:
As we move down Group 17 (Halogens: \(F, Cl, Br, I, At\)), a new principal energy level (shell) is added at each successive element.
Although the nuclear charge increases, the effect of the additional shells outweighs the increased nuclear pull.
The inner shells also provide a "shielding effect," reducing the attraction between the nucleus and the valence electrons.
Consequently, the outermost electrons are further from the nucleus, leading to an increase in atomic size.
Step 4: Final Answer: The atomic radii of group 17 elements increase down the group due to the addition of new shells.