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 Cu_1.997S to Cu_2.000S.^[4] Samples are typically black.

Copper(I) sulfide

Names
IUPAC name Copper(I) sulfide
Other names Cuprous sulfide Chalcocite Copper glance
Identifiers
CAS Number	22205-45-4 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:51114 Y
ChemSpider	8305611 Y
ECHA InfoCard	100.040.751
PubChem CID	62755
RTECS number	GL8910000
UNII	349M3C1RS1 Y
CompTox Dashboard (EPA)	DTXSID0041804
InChI InChI=1S/2Cu.S/q2*+1;-2 Y Key: AQMRBJNRFUQADD-UHFFFAOYSA-N Y InChI=1/2Cu.S/q2*+1;-2 Key: AQMRBJNRFUQADD-UHFFFAOYAN
SMILES [Cu+].[Cu+].[S-2]
Properties
Chemical formula	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]
Solubility in water	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). Y verify (what is YN ?) 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 Cu_1.96S, this material is non-stoichiometric (range Cu_1.934S-Cu_1.965S) and has a monoclinic structure with 248 copper and 128 sulfur atoms in the unit cell.^[7] Cu₂S and Cu_1.96S 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

• Copper sulfide for an overview of all copper sulfide phases
• Copper monosulfide, CuS
• Chalcocite
• Djurleite
• LK-99 - compound evaluated in 2023 for possible superconductivity

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. Bibcode:1977EcGeo..72.1524P. 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 (Cu_1.94S) and Low Chalcocite (Cu₂S): New Crystal Structure Studies". Science. 203 (4378): 356–8. Bibcode:1979Sci...203..356E. doi:10.1126/science.203.4378.356. PMID 17772445. S2CID 6132717.
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. 620 (7975): 705–706. Bibcode:2023Natur.620..705G. doi:10.1038/d41586-023-02585-7. PMID 37587284. S2CID 260955242.
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).