Rank the following elements by electron affinity, from most positive to most negative EA value: Na, Cl, S, Ar.

• A. Na > Ar > Cl > S
• B. Ar > Na > S > Cl
• C. Cl > S > Na > Ar
• D. S > Cl > Na > Ar

Answer: (B)

Verified step by step guidance

1. Understand that electron affinity (EA) is the energy change when an atom gains an electron. A more negative EA value means the atom releases more energy and has a stronger tendency to gain an electron.
2. Recall the general trends in the periodic table: EA tends to become more negative across a period from left to right, because atoms more strongly attract additional electrons as their nuclear charge increases.
3. Consider the elements given: Na (Group 1), Cl (Group 17), S (Group 16), and Ar (Group 18). Argon is a noble gas with a full valence shell, so it typically has a positive or less negative EA (it does not tend to gain electrons).
4. Rank the elements by comparing their positions: Cl is expected to have the most negative EA (strongest electron affinity), followed by S, then Na, and finally Ar with the least negative or even positive EA.
5. Use this reasoning to order the elements from most positive EA (least tendency to gain electrons) to most negative EA (greatest tendency to gain electrons) as: Ar > Na > S > Cl.