Question

The electronic configuration of Cu is ${ 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 6 }{ 3s }^{ 2 }{ 3p }^{ 6 }{ 4s }^{ 1 }{ 3d }^{ 10 }$. How many valence electrons does copper contain?
(A) ${ 1 }$
(B) ${ 2 }$
(C) ${ 8 }$
(D) ${ 11 }$

Answer 1

Hint: In an atom, the electrons are present in shells. The number of electrons in the last shell of an atom is known as valence electrons.

Complete step-by-step answer:
- The expected configuration of Cu is ${ 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 6 }{ 3s }^{ 2 }{ 3p }^{ 6 }{ 4s }^{ 2 }{ 3d }^{ 9 }$
- But as we know that the half-filled and fully-filled configuration gets extra stability. So, one of the electrons of ${ 4s }^{ 2 }$ jumps to ${ 3d }^{ 9 }$.
Hence, the correct electronic configuration of Cu is ${ 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 6 }{ 3s }^{ 2 }{ 3p }^{ 6 }{ 4s }^{ 1 }{ 3d }^{ 10 }$.
As we see here, the valence shell of copper is the fourth shell. Thus total core electrons for electrons in the ${ 4s }$ subshell are its core electrons.
So, copper has ${ 1 }$ electrons in its fourth shell. Hence, copper has one valence electron.
The correct option is A.

Additional Information: Electronic configuration is the arrangement of electrons in the atomic or molecular orbitals of atoms or molecules. This arrangement of electrons, into different shells and subshells, is called electronic configuration.
- Aufbau principle states that: In the ground state of the atoms, the orbital is filled in increasing order of their energies. i.e electrons first occupy the lowest energy orbital available to them and enter in the higher energy orbital only after the lower energy orbitals are filled.
The order in which the electrons are filled in :
${ 1s }, { 2s }, { 2p }, { 3s }, { 3p }, { 4s }, { 3d }, { 4p }, { 5s }, { 4d }, { 5p }, { 6s }, { 4f }, { 5d }, { 6p }$.. and so on

Note: The possibility to make a mistake is that you may consider the incorrect electronic configuration despite the right one. One electron jumps from ${ 4s }$ to ${ 3d }$ for extra stability.