Question

Why CuCl2 is green but Cu2Cl2 is colourless?

Answer 1

In CuCl2, copper exists as divalent Cu2+ ions with 3d9 configuration. The presence of one unpaired electron in a 3d orbital accounts for its colour.

In Cu2Cl2, copper is monovalent with completely filled 3d orbitals with 10 electrons. There is no unpaired electron available for transition by absorption of light in the visible region.

Answer 2

CuCl2 is green but Cu2Cl2 is colourless because:

• Cu is in a +2 oxidation state in CuCl2 while Cu is in a +1 oxidation state in Cu2Cl2.
• The electronic configuration of a Cu is [Ar]18 3d10 4s1.
• So, the electronic configuration of a Cu+ is [Ar]18 3d10, but the electronic configuration of a Cu2+ is [Ar]18 3d9.
• As we know, Compounds having elements with 0 and 10 electrons in 3d shells are colourless.
• So, CuCl2 has 9 electrons in d orbitals while Cu2Cl2 has 10 electrons in ints d orbital.

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