Multiple Choice
Which of the following best describes the general trend for electron affinity values as you move from left to right across a period in the periodic table?
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10. Periodic Properties of the Elements
Periodic Trend: Electron Affinity
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Which of the following elements has the largest (most exothermic) first electron affinity (EA\(_1\))?
A
O
B
Ar
C
Na
D
Cl
Verified step by step guidance1
Understand that the first electron affinity (EA\(_1\)) is the energy change when an atom in the gas phase gains an electron to form an anion. A more exothermic (more negative) EA means the atom more readily accepts an electron.
Recall the general periodic trend: electron affinity becomes more exothermic across a period from left to right, reaching a maximum near the halogens, and becomes less exothermic down a group.
Analyze the given elements: O (oxygen) is a group 16 element, Ar (argon) is a noble gas in group 18, and Na (sodium) is an alkali metal in group 1. Cl (chlorine), the correct answer, is a halogen in group 17.
Recognize that halogens like Cl have the highest (most exothermic) electron affinities because they are one electron short of a full octet, making them very eager to gain an electron.
Conclude that among the given options, Cl has the largest (most exothermic) first electron affinity due to its position in the periodic table and its electronic configuration.
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