Quantum Numbers
Effective nuclear charge (Z_eff) experienced by valence electrons increases across a period mainly because:
Select the correct option:
Solution
Nuclear charge increases faster than shielding
- Definition: Zeff=Z−σ, where Z is the actual nuclear charge (number of protons) and σ is the shielding constant.
- Trend across Period: As we move from left to right, one proton is added to the nucleus for each consecutive element.
- Shielding Factor: Electrons are added to the same main valence shell. These electrons do not shield each other very effectively compared to inner-core electrons.
- Outcome: The increase in Z far outweighs the slight increase in shielding from same-shell electrons.
- Result: Valence electrons feel a stronger pull towards the nucleus, leading to a higher Zeff and a decrease in atomic radius.
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About This Question
- Subject
- chemistry
- Chapter
- atomic structure
- Topic
- quantum numbers
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
Nuclear charge increases faster than shielding
- Definition: Zeff=Z−σ, where Z is the actual nuclear charge (number of protons) and σ is the shielding constant.
- Trend across Period: As we move from left to right, one proton is added to the nucleus for each consecutive element.
- Shielding Factor: Electrons are added to the same main valence shell. These electrons do not shield each other very effectively compared to inner-core electrons.
- Outcome: The increase in Z far outweighs the slight increase in shielding from same-shell electrons.
- Result: Valence electrons feel a stronger pull towards the nucleus, leading to a higher Zeff and a decrease in atomic radius.
This easy difficulty chemistry question is from the chapter atomic structure, covering the topic of quantum numbers. It appeared in the 2025 exam.
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