The compound with the chemical formula CuS is known by the systematic name Copper(II) Sulfide. This binary compound of copper and sulfur has attracted attention across multiple scientific disciplines due to its unique physical properties and complex internal structure. CuS is important in geology, where it exists as a naturally occurring mineral, and in materials science, where its semiconducting characteristics are utilized in advanced technologies. Its relevance spans from being a naturally occurring copper ore to its use in cutting-edge nanotechnology applications.
Official Chemical Nomenclature and Structure
The official chemical name for the compound CuS is Copper(II) Sulfide, a name derived from the rules for naming ionic compounds containing transition metals. Copper, symbolized as Cu, is a transition metal that can form ions with more than one possible positive charge, specifically +1 or +2. The Roman numeral “(II)” indicates that the copper ion in this specific compound carries a charge of positive two, or Cu²⁺. The compound is formed by the electrostatic attraction between the Cu²⁺ cation and the sulfide anion, S²⁻, where sulfur has a charge of negative two. The charges balance out in a one-to-one ratio, resulting in the empirical formula CuS.
Older or less formal names, such as cupric sulfide or copper monosulfide, are sometimes used. However, the systematic name is preferred for clarity to distinguish it from copper(I) sulfide (Cu₂S). The molar mass of CuS is approximately 95.61 grams per mole.
The crystal structure of CuS is complex and deviates from a simple ionic lattice. It crystallizes in the hexagonal system, which is the form found in the mineral covellite. Analysis reveals that it is not purely Cu²⁺ and S²⁻, but contains copper with different oxidation states and both monosulfide (S²⁻) and disulfide (S₂²⁻) units. The formula is more accurately represented as Cu₃S(S₂), indicating an intricate bonding arrangement.
Key Physical and Chemical Characteristics
Copper(II) Sulfide is typically observed as a dark solid, often described as black or indigo-blue in its crystalline form. The density of the compound is relatively high, measured at approximately 4.76 g/cm³. This dense, dark appearance is characteristic of many metal sulfides.
A key chemical property of CuS is its insolubility in water and dilute acids. This low solubility is common among heavy metal sulfides and is utilized in chemical separation processes. When heated, CuS undergoes thermal decomposition at approximately 220 °C instead of melting. The compound is stable in dry air, but exposure to moist air causes a slow oxidation reaction, gradually forming copper(II) sulfate (CuSO₄). This reactivity requires consideration for the long-term storage and handling of the material.
Natural Presence and Industrial Applications
In nature, CuS occurs as the mineral covellite, an important copper-bearing ore typically found in copper deposits. Covellite is known for its striking indigo-blue color and sub-metallic luster. The geological significance of covellite lies in its role as a secondary copper sulfide, often formed through the weathering and alteration of other copper minerals.
The synthetic form of Copper(II) Sulfide has a wide range of applications, spanning from traditional uses to advanced materials science. Historically, CuS was utilized as a pigment, known as Copper Blue, due to its deep color. In modern industry, its high energy capacity and good electronic conductivity make it a suitable material for use as a cathode in lithium batteries.
In the field of nanotechnology, CuS nanoparticles are highly valued for their unique optical and electronic traits. Copper(II) Sulfide is classified as a p-type semiconductor, meaning its electrical conductivity is dominated by positively charged “holes.” This characteristic, combined with its high absorption coefficient, makes it promising for use in solar cells and other optoelectronic devices. Furthermore, the nanoparticles exhibit a localized surface plasmon resonance (LSPR) in the near-infrared region, allowing them to efficiently convert light energy into heat. This photothermal effect is being actively researched for use in biomedical applications, such as photothermal therapy for cancer and targeted drug delivery systems.