QuestionAugust 12, 2025

2. Why is [Ar]4s^24d^104p^4 the incorrect electron configuration for selenium?

2. Why is [Ar]4s^24d^104p^4 the incorrect electron configuration for selenium?
2. Why is [Ar]4s^24d^104p^4 the incorrect electron configuration for selenium?

Solution
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Answer

The incorrect configuration places electrons in the 4d orbital before the 3d, violating the Aufbau principle. The correct configuration is [Ar]3d^{10}4s^{2}4p^{4}. Explanation 1. Identify the correct order of electron filling Electrons fill orbitals in order of increasing energy, following the Aufbau principle. The correct sequence is 4s, then 3d, and finally 4p. 2. Determine the correct configuration for selenium Selenium has an atomic number of 34. The correct electron configuration should be [Ar]3d^{10}4s^{2}4p^{4}, not [Ar]4s^{2}4d^{10}4p^{4}.

Explanation

1. Identify the correct order of electron filling<br /> Electrons fill orbitals in order of increasing energy, following the Aufbau principle. The correct sequence is $4s$, then $3d$, and finally $4p$.<br /><br />2. Determine the correct configuration for selenium<br /> Selenium has an atomic number of 34. The correct electron configuration should be $[Ar]3d^{10}4s^{2}4p^{4}$, not $[Ar]4s^{2}4d^{10}4p^{4}$.
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