Chapter 6, Problem 80A

Interpretation Introduction

Interpretation:

It is to be explained why atomic size increases from top to bottom and decreases across the period.

Concept Introduction :

Periodic trends are patterns found in the periodic table that show several facets of a particular element. A periodic trend is observed in atomic size also.

Explanation of Solution

Atomic size increases down the group. This is because when moving from top to bottom in the group, both the number of shells and nuclear charge increase. The effect of more shells, however, outweighs the effect of a higher nuclear charge which increases atomic radius.

Whereas atomic size decreases across the period or decreases from left to right. This is because when moving left to right in the periodic table, the number of shells stays constant while the nuclear charge increases by one at each step. As nuclear charge increases, electrons in the outermost shell are drawn to it with increasing force, which causes the size of atoms to gradually shrink over time.