Question

Why CuCl2 is blue coloured but CuCl is colourless

Answer 1

because the first compound exists as a complex ion and has d-d transitions.

Answer 2

$CuCl_2$ contains unpaired electrons whereas $CuCl$ does not contain unpaired electrons.

Explanation:

Atomic number of copper is 29.

The electronic configuration of copper will be,

$1s^22s^23s^23p^64s^13d^{10}$

The electronic configuration of $Cu^+$ in $CuCl$ will be,

$Cu^+:1s^22s^23s^23p^63d^{10}$

The electronic configuration of $Cu^{2+}$ in $CuCl_2$ will be,

$Cu^{2+}:1s^22s^23s^23p^63d^{9}$

As we know that the unpaired electrons present in the $Cu^{2+}$ ion show blue color due to the transition of the electrons from ground state to the excited state.

In case of $Cu^+$ there is no unpaired electrons that means the shells are fully filled. So, it will not show any color. That's why $CuCl$ is colorless.

Learn more about transition elements

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