How do atomic radii vary in a period and in a group? How do you explain the variation?

Explanation

To understand how atomic radii vary in a period and in a group, we need to analyze the trends and the reasons behind these variations.

### Step-by-Step Solution:

**Step 1: Variation of Atomic Radii in a Group**
- When moving down a group in the periodic table (for example, from Lithium to Cesium in Group 1), the atomic radii increase.
- This increase occurs because as you move down a group, each successive element has an additional electron shell (energy level). For instance, Lithium has 2 shells, while Cesium has 6 shells.

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