Question

The electronic configuration of valence shell of Cu is $3{{d}^{10}}4{{s}^{1}}$ and not $3{{d}^{9}}4{{s}^{2}}$. How is this configuration explained?

Answer 1

Hint: As we know that Cu is the chemical symbol of the copper element which belongs to the d-block of the periodic table. Electronic configuration of an element gives us information about the number of electrons which are distributed in its atomic orbitals. So here we have to explain the reason behind the abnormal electronic configuration of valence shell of Copper which is $3{{d}^{10}}4{{s}^{1}}$ and not $3{{d}^{9}}4{{s}^{2}}$.

Complete answer:
Let us discuss about electronic configuration followed by copper element and its abnormal electronic configuration as follows:-
-Electron configuration: It describes the number of electrons that are distributed in the atomic orbitals of different elements. It follows a standard notation in which all atomic sub-shells containing electrons are placed in a sequence with the number of electrons they hold (these are written in superscript).
-Copper: It is a chemical element denoted by the symbol Cu and has atomic number 29. It is soft, shiny, malleable, and ductile transition metal with extremely high thermal and electrical conductivity. The observed electron configuration of Cu is: $[Ar]3{{d}^{10}}4{{s}^{1}}$ whereas the expected electronic configuration is $[Ar]3{{d}^{9}}4{{s}^{2}}$.
-This electronic configuration of Cu is different than the common trend (i.e., filling s subshell and then d sub-shell) due to the full filled stability of d sub-shell which copper achieves when electron jump from orbital of s- subshell to the orbital of d sub-shell (an electron can jump from a sub-shell of lower energy (4s) to a sub-shell of a higher energy (3d) if there is only slight difference in their energies.)
-The full filled stability of Cu is because of the following two reasons:-
Exchange energy: In d-subshell, there are 5 orbitals due to which ten exchanges of electrons are possible that imparts much stability to copper. Therefore this process is exothermic in nature as well.
Also the symmetrical distribution of electrons in 3 dimensional space also imparts much stability to copper due a full d subshell.
Therefore, the observed electron configuration of valence shell of Cu is $3{{d}^{10}}4{{s}^{1}}$ and not $3{{d}^{9}}4{{s}^{2}}$.

Note:
-Remember that the same abnormal electronic configuration can be seen in the case of Chromium metal which is also a transition metal. We can observe half-filled stability of d sub-shell in its case ($[Ar]3{{d}^{5}}4{{s}^{1}}$ ) due to which an electron jumps from a sub-shell of lower energy (4s) to a sub-shell of higher energy (3d).
-Also the full electronic configuration of copper is: $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}3{{d}^{10}}4{{s}^{1}}$.