Chemistry Answered
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Aufbau principle, electronic configuration

Why does the 4s orbital fill before 3d?

Isn’t 3d supposed to come first?
Admin User
Asked 1 week ago
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Answers (1)
Admin User
Answered 2025 years ago
It’s because the energy of 4s is slightly lower than 3d due to shielding and penetration effects. Hence, electrons prefer 4s before 3d when filling.
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