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zinc sulphide and other chalcogen compounds of the Zn,Cd and Hg group

I recently purchased a cadmium sulphide light dependant resistor for an electronics project, This made me think about the compounds which can be formed from zinc, cadmium and mercury with oxygen, sulphur, selenium or tellurium.

Zinc oxide is known as zincite, this is hexagonal solid.

Zinc sulphide is known as wurtzite which is also a hexagonal solid, but it also comes in a cubic form known as sphalerite. For the selenide and telluride of zinc both hexagonal and cubic forms are known.

Cadmium oxide, the sulphide and the selenide can be found in both a hexagonal (wurtzite) and cubic (sodium chloride type) forms. Cadmium telluride can be found in both the hexagonal (wurtzite) form and in a cubic form like zinc sulphide.

II have not got onto the mercury compounds, but I hope to be able to do the maths with you to work out why different metal / chalcogen conbinations give different solids.

While you are waiting here is a film to watch of me making some cadmium sulphide by treating cadmium nitrate solution with hydrogen sulphide.

Those of you who have good colour vision will have noticed that the product is yellow. It is important to understand that as a d10 metal ion the Cd(II) centre is colourless. The reason it is coloured is that the solid is a semiconductor, when the light falls on it electrons are moved into a conduction band. Hence it is yellow not white.


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