Question

Electronic configuration of copper (atomic No. \[{\text{Cu}} - 29\] ) is:
A. \[1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^8}4{s^2}4{p^1}\]
B. \[1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^9}4{s^1}4{p^1}\]
C. \[1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^8}4{s^1}4{p^1}\]
D. \[1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^1}4{p^0}\]

Answer 1

Hint:According to the Aufbau principle, electrons first occupy the atomic orbitals having lowest energy levels. Once these atomic orbitals are filled, then electrons enter higher energy levels.

Complete answer:
You can follow the Aufbau principle to determine the sequence of filling the electrons in the order of sub-energy levels s,p,d and f. In German language, the word Aufbau means building up. This rule is helpful in determining the electronic configuration of atoms/ions.

The atomic number of Argon is \[18\]. The electronic configuration of argon is \[{\text{2}},{\text{8}},{\text{8}}\] . It can also be written as \[1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}\]. The electronic configuration of copper having atomic number \[29\] is \[{\text{2}},{\text{8}},{\text{ 18}},{\text{ 1}}\]. It can also be written as \[1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^1}4{p^0}\].or \[\left[ {{\text{Ar}}} \right]3{d^{10}}4{s^1}4{p^0}\].

The expected electronic configuration of copper is \[\left[ {{\text{Ar}}} \right]3{d^9}4{s^2}4{p^0}\] . But the observed electron configuration of copper is \[\left[ {{\text{Ar}}} \right]3{d^{10}}4{s^1}4{p^0}\].The observed electron configuration of \[\left[ {{\text{Ar}}} \right]3{d^{10}}4{s^1}4{p^0}\] is more stable than the expected electronic configuration of \[\left[ {{\text{Ar}}} \right]3{d^9}4{s^2}4{p^0}\]. This is due to extra stability of half-filled and completely filled subshells.

In the expected electron configuration, the 3d subshell contains 9 electrons and is partially filled. Hence, it is less stable. In the observed electron configuration, the 3d subshell contains 10 electrons and is completely filled. Hence, it is more stable. In both expected and observed electronic configurations, the 4s subshell is stable as it is either half filled or completely filled.

Hence the correct answer is option ‘B’.

Note:While filling the electrons into various subshells, the order \[1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p\] is based on the following points. Higher is the \[\left( {{\text{n + l}}} \right)\] value of an orbital, higher is its energy. Lower is the \[\left( {{\text{n + l}}} \right)\] value of an orbital, lower is its energy. When two orbitals have equal value of \[\left( {{\text{n + l}}} \right)\] then the orbital having higher value of n will have higher energy. The principal quantum number, ‘n’ can have values 1,2,3,4…. The azimuthal quantum number can have values 0,1,2,3…