Which one among the following is the correct ground state electronic c

Which one among the following is the correct ground state electronic configuration of Cr atom ?

[amp_mcq option1=”1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁴ 4s²” option2=”1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹” option3=”1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s⁰” option4=”1s² 2s² 2p⁶ 3s² 3p³ 4s²” correct=”option2″]

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UPSC Geoscientist – 2024

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The correct ground state electronic configuration of a Cr (Chromium) atom is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹.

Chromium (atomic number 24) is an exception to the standard Aufbau principle filling order. The configuration 3d⁵ 4s¹ is more stable than 3d⁴ 4s² due to the enhanced stability of a half-filled d subshell.

The electronic configuration follows the Aufbau principle generally, filling orbitals in increasing order of energy (1s, 2s, 2p, 3s, 3p, 4s, 3d…). However, for chromium and copper, promotion of an electron from the 4s orbital to the 3d orbital leads to half-filled (d⁵) or fully filled (d¹⁰) d subshells, which are particularly stable arrangements. The full configuration starts with the filled inner shells (equivalent to Argon, [Ar]), which is 1s² 2s² 2p⁶ 3s² 3p⁶, followed by 3d⁵ 4s¹.

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