Copper(I) sulfide is an inorganic compound with the formula Cu₂S. This compound is classified as an ionic salt, formed by the electrostatic attraction between positively charged copper ions and negatively charged sulfide ions. In nature, Cu₂S is the primary component of the mineral chalcocite, also known as copper glance, which has historically been a significant source for copper metal extraction.
Translating Ionic Names into Formulas
The chemical name Copper(I) Sulfide provides the information needed to construct the formula, relying on the principle of electrical neutrality. The name’s second part, “sulfide,” indicates the sulfur ion, which consistently carries a -2 charge (S²⁻).
The Roman numeral (I) specifies the charge of the copper ion as +1 (Cu⁺). For the compound to be stable, the total positive charge must exactly balance the total negative charge, resulting in a net charge of zero. Since the sulfide ion has a charge of -2, it requires two Cu⁺ ions to achieve this balance.
This requirement for two copper ions to one sulfide ion is the chemical logic behind the formula Cu₂S. The subscript “2” next to copper signifies that two copper atoms are present for every one sulfur atom. This simple ratio ensures the overall compound is electrically neutral, a fundamental requirement for all stable ionic compounds.
The Significance of the Roman Numeral
The Roman numeral in Copper(I) Sulfide is included because copper is a transition metal that can form ions with more than one positive charge. Without this designation, the name “Copper Sulfide” would be ambiguous. The Stock nomenclature system uses Roman numerals to indicate the specific oxidation state of the metal component.
The numeral (I) distinguishes this compound from Copper(II) Sulfide, which has the formula CuS. In the Copper(II) variant, the copper ion carries a +2 charge (Cu²⁺), which balances the -2 charge of a single S²⁻ ion in a simple 1:1 ratio. The two compounds, Cu₂S and CuS, possess distinct chemical structures and properties.
Physical Characteristics and Applications
Cu₂S is a black or dark indigo crystalline solid. This material has low solubility, being nearly insoluble in water, though it can decompose when exposed to strong acids like nitric acid.
The compound has industrial relevance, particularly as a semiconductor material. Its ability to conduct electricity makes it suitable for use in photo-optic applications, including the manufacturing of photovoltaic cells, or solar panels. Beyond its role in modern electronics, its natural form, chalcocite, remains a primary ore for the global production of metallic copper.