Copper(I) sulfide

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.[4] Samples are typically black.

Copper(I) sulfide
Names
IUPAC name
Copper(I) sulfide
Other names
Cuprous sulfide
Chalcocite
Copper glance
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.040.751
RTECS number
  • GL8910000
UNII
  • InChI=1S/2Cu.S/q2*+1;-2 checkY
    Key: AQMRBJNRFUQADD-UHFFFAOYSA-N checkY
  • InChI=1/2Cu.S/q2*+1;-2
    Key: AQMRBJNRFUQADD-UHFFFAOYAN
  • [Cu+].[Cu+].[S-2]
Properties
Cu2S
Molar mass 159.16 g/mol
Density 5.6 g/cm3 [1]
Melting point 1,130 °C (2,070 °F; 1,400 K)[2]
insoluble
Solubility slightly soluble in HCl; soluble in NH4OH; dissolves in KCN; decomposes in HNO3, H2SO4
Hazards
Flash point Nonflammable
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 1 mg/m3 (as Cu)[3]
REL (Recommended)
 TWA 1 mg/m3 (as Cu)[3]
IDLH (Immediate danger)
 TWA 100 mg/m3 (as Cu)[3]
Related compounds
Other anions
 Copper(I) oxide
Copper(I) selenide
Other cations
 Nickel(II) sulfide
Copper(II) sulfide
Zinc sulfide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Preparation and reactions

Cu2S can be prepared by treating copper with sulfur or H2S.[2] The rate depends on the particle size and temperature.[5] Cu2S reacts with oxygen to form SO2:[6]

2 Cu2S + 3 O2 → 2 Cu2O + 2 SO2

The production of copper from chalcocite is a typical process in extracting the metal from ores. Usually, the conversion involves roasting, to give Cu2O and sulfur dioxide:[6]

Cu2S + O2 → 2 Cu + SO2

Cuprous oxide readily converts to copper metal upon heating.

Structure
Crystals of chalcocite (mineral form of Cu2S).

Stoichiometric

Two forms (a dimorphism) of Cu2S are known. The so-called low temperature monoclinic form ("low-chalcocite") has a complex structure with 96 copper atoms in the unit cell.[7] The hexagonal form, stable above 104 °C,[8] has 24 crystallographically distinct Cu atoms. Its 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.

Non-stoichiometric

As illustrated by the mineral djurleite, a cuprous sulfide is also known. With the approximate formula Cu1.96S, this material is non-stoichiometric (range Cu1.934S-Cu1.965S) and has a monoclinic structure with 248 copper and 128 sulfur atoms in the unit cell.[7] Cu2S and Cu1.96S are similar in appearance and hard to distinguish one from another.[9]

Phase transition

The electrical resistivity increases abruptly at the phase transition point around 104 °C, with the precise temperature depending on the stoichiometry.[10][11]

See also

References
  1. Patnaik, Pradyot (2002). Handbook of Inorganic Chemicals. McGraw-Hill, ISBN 0-07-049439-8
  2. Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. p. 1373. ISBN 978-0-08-022057-4.
  3. NIOSH Pocket Guide to Chemical Hazards. "#0150". National Institute for Occupational Safety and Health (NIOSH).
  4. Potter, R. W. (1977). "An electrochemical investigation of the system copper-sulfur". Economic Geology. 72 (8): 1524–1542. doi:10.2113/gsecongeo.72.8.1524.
  5. Blachnik R., Müller A. (2000). "The formation of Cu2S from the elements I. Copper used in form of powders". Thermochimica Acta. 361: 31. doi:10.1016/S0040-6031(00)00545-1.
  6. Wiberg, Egon and Holleman, Arnold Frederick (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5
  7. Evans, H. T. (1979). "Djurleite (Cu1.94S) and Low Chalcocite (Cu2S): New Crystal Structure Studies". Science. 203 (4378): 356–8. doi:10.1126/science.203.4378.356. PMID 17772445.
  8. Wells A.F. (1984) Structural Inorganic Chemistry, 5th ed., Oxford Science Publications, ISBN 0-19-855370-6
  9. Evans H.T. (1981). "Copper coordination in low chalcocite and djurleite and other copper-rich sulfides" (PDF). American Mineralogist. 66 (7–8): 807–818.
  10. Garisto, Dan (2023-08-16). "LK-99 isn't a superconductor — how science sleuths solved the mystery". Nature. doi:10.1038/d41586-023-02585-7.
  11. Jain, Prashant K. "Phase transition of copper (I) sulfide and its implication for purported superconductivity of LK-99." arXiv preprint arXiv:2308.05222 (2023).
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