Of the following elements, which would you expect to have the largest electron affinity?

• A. Na
• B. Cl
• C. Si
• D. Mg

Answer: (B)

Verified step by step guidance

1. Understand that electron affinity is the energy change that occurs when an atom gains an electron, typically releasing energy (exothermic). Elements with higher electron affinity values tend to attract electrons more strongly.
2. Recall the general trend of electron affinity in the periodic table: it increases across a period from left to right and generally decreases down a group. This is because atoms on the right side of the periodic table have more effective nuclear charge and smaller atomic radii, making it easier to attract an additional electron.
3. Identify the positions of the given elements in the periodic table: Sodium (Na) is in Group 1, Period 3; Magnesium (Mg) is in Group 2, Period 3; Silicon (Si) is in Group 14, Period 3; Chlorine (Cl) is in Group 17, Period 3.
4. Compare their electron affinities based on their group positions: since Cl is a halogen (Group 17), it has a much higher tendency to gain an electron compared to Na, Mg, and Si, which are farther left in the same period.
5. Conclude that Chlorine (Cl) has the largest electron affinity among the given elements because it is closest to filling its valence shell and strongly attracts an additional electron.