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in Structure of Atom by (30.3k points)
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A student argued that the 3d orbitals will be filled only after the 4s orbital is completely filled in accordance with aufbau principle. Then another student opposed by saying that it is not true for certain elements like Cr and Cu. 

(a) Whose argument is correct? 

(b) Write electronic configurations of 24Cr and 29Cu. Justify your answer.

1 Answer

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Best answer

(a) Both arguments are correct. 

(b) Cr and Cu have anomalous electronic configurations. This is because half filled and completely filled sub-shells have extra stability due to the symmetrical distribution of electrons maximum exchange energy. 

24Cr = 1 s2 2s2 2p6 3s2 3p6 3d5 4s1 

OR

[Ar]3d5 4s1 This is due to the extra stability of half filled 3d5 sub-shell.

29Cu = 1 s2 2s2 2p6 3s2 3p6 3d5 4s1 

OR

[Ar]3d10 4s1This is due to the extra stability of completely filled 3d10 sub-shell.

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