Cr has a configuration of 3d⁵ 4s¹ instead of 3d⁴ 4s², and Cu has 3d¹⁰ 4s¹ instead of 3d⁹ 4s². The small energy gap between 3d and 4s orbitals prevents electrons from entering the 3d orbitals, contributing to these unique configurations.
Explain the deviation in electronic configuration for Cr and Cu in the 3d series, and what prevents electrons from entering the 3d orbitals in these cases?
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The deviation in electronic configuration for Cr and Cu in the 3d series is due to the stability associated with half-filled and completely filled sets of orbitals. In the case of Chromium (Cr), it has an electronic configuration of 3d⁵ 4s¹ instead of the expected 3d⁴ 4s². This deviation occurs because the energy gap between the 3d and 4s orbitals is small, preventing an electron from entering the 3d orbitals. Similarly, Copper (Cu) exhibits a configuration of 3d¹⁰ 4s¹ instead of 3d⁹ 4s². The stability conferred by a fully filled 3d orbital prevents additional electrons from entering the 3d orbitals.