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Copper forms two chlorides CuCl and $CuCl_{ 2 }$.
(a) Identify the copper ions in these compounds?
(b) What is the valency of copper in each of these compounds?
(c) By writing the subshell electronic configuration of copper, find out the subshells from which the electrons are lost to form these ions.
(d) Write the period and group to which copper belongs.
(Hint: Atomic number of Copper=29)

Answer
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Hint: Find the valency of copper ions by taking other atoms in their general form. Follow the principles of electronic configuration. Copper belongs to the d-block in the periodic table. By considering the number of electrons in the d-subshell calculate the group number. By the electronic configuration of copper, we can decide to which period it belongs.

Complete answer:
We know that copper exhibits more than one oxidation state. The total charge on compound CuCl is 0. And the general valency of copper is -1. The number of chlorine atoms is 1. So the charge of copper will be +1. It is the lower oxidation state of copper so the compound will be called cuprous chloride. Valency of copper in CuCl is +1.
The total charge on $CuCl_{ 2 }$ is 0. And the general valency of copper is -1. The number of chlorine atoms is 2. So the charge of copper will be +2. It is the higher oxidation state of copper. The compound is called cupric chloride. Cupric ions form a precipitate when reacted with hydrogen sulfide. It forms a blue color complex in the presence of aqueous ammonia.
Copper has 29 electrons in its neutral form. It has d subshell electrons. Electronic configuration of copper is $1s^{ 2 }2s^{ 2 }2p^{ 6 }3s^{ 2 }3p^{ 6 }3d^{ 10 }4s^{ 1 }$.
Configuration $Cu^{ + }$ ion is $1s^{ 2 }2s^{ 2 }2p^{ 6 }3s^{ 2 }3p^{ 6 }3d^{ 10 }$. Electrons are lost from the 4s subshell.
Configuration $Cu^{ +2 }$ ion is $1s^{ 2 }2s^{ 2 }2p^{ 6 }3s^{ 2 }3p^{ 6 }3d^{ 9 }$. Electrons are lost from the 3d subshell.
Copper belongs to the fourth period. It belongs to the eleventh group.

Note: Cupric ion is more stable than cuprous ion so copper exists in the +2 oxidation state. In copper, electronic configuration copper has 3d subshell filled before 4s because when inner shells are completely filled they attain more stability.