The electron configuration for $\mathrm{Cu}$is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{1}3{\mathrm{d}}^{10}$. How many valence electrons does Copper contain?

Valence Electrons:

• The number of electrons present in the outermost or last shell of an atom is known as its valence electrons.
• The number of valence electrons present in a given molecule, mostly also represents its group number.

Valence electrons of Copper :

• The ground state electronic configuration of $\mathrm{Cu}$ is given as:${1\mathrm{s}}^2{2\mathrm{s}}^2{2\mathrm{p}}^6{3\mathrm{s}}^2{3\mathrm{p}}^6{4\mathrm{s}}^2{3\mathrm{d}}^9$.
• But as we know that the half-filled and fully-filled configuration gets extra stability. So, one of the electrons of ${4s}^2$ get jumped into ${3d}^9$.
• Which forms the exciting electronic configuration of Cu as:${1\mathrm{s}}^2{2\mathrm{s}}^2{2\mathrm{p}}^6{3\mathrm{s}}^2{3\mathrm{p}}^6{4\mathrm{s}}^2{3\mathrm{d}}^9$.
• As we see here, the valence shell of copper is the fourth shell, thus the total electrons present in the $4s$ subshell are its valence electrons.
• Hence, copper has $1$ electrons as its valence electron.

Thus, the number of valence electrons that copper contain is $1$.