Questions: Periodic Trends: Size and Reactivity Patterns

Question 1

As you move down a group on the periodic table, what happens to atomic size?

• A. It decreases
• B. It stays the same
• C. It increases
• D. It alternates

Answer: (C)

Atomic size increases moving down a group because each row adds a new electron energy level (shell), making the atom physically larger. The outermost electrons are farther from the nucleus.

Question 2

Fluorine is more reactive than iodine because it is higher in Group 17.

• T. True
• F. False

Answer: True

For nonmetals (like the halogens in Group 17), reactivity increases going up the group. Fluorine is at the top and is the most reactive nonmetal because its small size and strong nuclear pull make it extremely effective at gaining electrons. Iodine, being much larger, holds incoming electrons less tightly and is less reactive.

Question 3

Explain why sodium is more reactive than magnesium, even though magnesium is right next to it on the periodic table.

Model answer: Sodium (Group 1) has only one valence electron to lose, making it easier to react. Magnesium (Group 2) has two valence electrons to lose, which requires more energy, making it less reactive.

Metal reactivity depends on how easily an atom gives up its valence electrons. Sodium needs to lose only 1 electron to achieve a stable arrangement, while magnesium needs to lose 2. Losing 2 electrons requires more energy, so magnesium reacts less readily than sodium. In general, Group 1 metals are more reactive than Group 2 metals in the same period.