Humber Admissions Practice Test

What is the trend in atomic size as you move down a group in the periodic table?

1. Increases from left to right

2. Decreases from top to bottom

3. Increases from top to bottom

4. Remains constant

The correct answer is: Increases from top to bottom

As you move down a group in the periodic table, atomic size increases. This trend occurs primarily due to the addition of electron shells. Each time you move down to the next element in a group, another electron shell is added, which increases the distance between the nucleus and the outermost electrons. This larger distance causes the atomic radius to expand, contributing to the increase in atomic size. Moreover, even though there is an increased positive charge in the nucleus (due to additional protons) as you move down a group, the effect of increased electron shielding (the repulsive effect of inner-shell electrons) reduces the effective nuclear charge felt by the outermost electrons. This also allows the outer electrons to be held less tightly by the nucleus, contributing to the increase in atomic size. The other options reflect misconceptions about atomic size trends. For example, the idea that atomic size increases from left to right is true across a period, but not down a group. The notion that atomic size decreases from top to bottom contradicts the established trend, and the concept of atomic size remaining constant does not account for the changes in electron shells at different energy levels.