Multiple Choice
Which one of the following atoms has the least tendency to gain another electron?
9. Electrons in Atoms and the Periodic Table
Periodic Trend: Electron Affinity (Simplified)
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Which element has the greatest electron affinity (most energy released when a neutral atom gains an electron) among the following?
A
Chlorine (Cl)
B
Bromine (Br)
C
Oxygen (O)
D
Fluorine (F)
Verified step by step guidance1
Understand the concept of electron affinity: it is the amount of energy released when a neutral atom gains an electron. A higher electron affinity means the atom more readily accepts an electron.
Recall the general periodic trend for electron affinity: it tends to increase across a period (left to right) because atoms have a stronger effective nuclear charge, attracting electrons more strongly.
Also consider the trend down a group (top to bottom): electron affinity generally decreases because added electron shells increase the distance between the nucleus and the added electron, reducing attraction.
Compare the given elements based on their positions in the periodic table: Oxygen (O) and Fluorine (F) are in period 2, with Fluorine to the right of Oxygen; Bromine (Br) and Chlorine (Cl) are in period 4 and 3 respectively, with Chlorine above Bromine.
Analyze the electron configurations and atomic structure to understand why Chlorine has a higher electron affinity than Fluorine despite Fluorine being to the right: Fluorine's small size causes electron-electron repulsion in its compact 2p orbitals, slightly lowering its electron affinity compared to Chlorine.
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