Formula Cu2S Melting point 1,130 °C | Molar mass 159.16 g/mol Density 5.6 g/cm³ | |
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Copper(I) sulfide is a copper sulfide, a chemical compound of copper and sulfur. It has the chemical compound Cu2S. It is found in nature as the mineral chalcocite. It has a narrow range of stoichiometry ranging from Cu1.997S to Cu2.000S.
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Preparation and reactions
Cu2S can be prepared by heating copper strongly in sulfur vapour or H2S. The reaction of copper powder in molten sulfur rapidly produces Cu2S, where as pellets of copper require much higher temperature. Cu2S reacts with oxygen to form SO2:
2 Cu2S + 3 O2 → 2 Cu2O + 2 SO2In the production of copper two thirds of the molten copper sulfide is oxidised as above, and the Cu2O reacts with unoxidised Cu2S to give Cu metal:
Cu2S + 2 Cu2O → 6 Cu + SO2Structure
There are two forms of Cu2S a low temperature monoclinic form ("low-chalcocite") which has a complex structure with 96 copper atoms in the unit cell and a hexagonal form stable above 104 °C. In this structure there are 24 crystallographically distinct Cu atoms and the structure has been described as approximating to a hexagonal close packed array of sulfur atoms with Cu atoms in planar 3 coordination. This structure was initially assigned an orthorhombic cell due to the twinning of the sample crystal.
There is also a crystallographically-distinct phase (the mineral djurleite) with stoichiometry Cu1.96S which is non-stoichiometric (range Cu1.934S-Cu1.965S) and has a monoclinic structure with 248 copper and 128 sulfur atoms in the unit cell. Cu2S and Cu1.96S are similar in appearance and hard to distinguish one from another.