CBSE Class 10 Science 2020 · Paper 31/3/1 · Question 2(b)
The atomic radii of first group elements are given below :
State the reason behind the observed trend in the above elements.
| Group-I element | Atomic Radii (pm) |
|---|---|
| Na | 86 |
| K | 231 |
| Rb | 244 |
| Cs | 282 |
Answer
Atomic radius increases from Na to Cs because a new shell is added at each step down the group.
The atomic radius increases from Na to Cs. This is because a new shell is added at each step down the group, so the outermost electrons are farther from the nucleus; the atomic size therefore increases in spite of the increase in nuclear charge.
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