Question

the outer electronic configuration of Cu is 3d¹⁰ 4s¹ one instead of 3d⁹ 4s² why?​

Answer 1

Explanation:

Argon is the noble gas with 18 electrons. As completely filled d-shell is more stable in nature. Hence, one electron from the 4s shell goes into the d-orbital so the copper atom can attain stability

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Answer 2

Answer:

The outer electronic configuration of Cu is 3d¹⁰ 4s¹  instead of 3d⁹ 4s²

Explanation:

This is because the atom Cu tries to fill it's inner shell first and make itself stable.

Thus, before filling it's valence shell Cu fills it's inner shell first

So it's configuration :

Cu: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹