Dioxid

Dioxid, or dioxide, refers to a class of chemical compounds that contain two oxygen atoms per formula unit. The term covers a wide range of substances, from simple molecular species such as carbon dioxide (CO2) and sulfur dioxide (SO2) to extended oxide networks such as silicon dioxide (SiO2) and titanium dioxide (TiO2). In many dioxides the central element is in a high oxidation state, commonly +4.

Dioxides vary widely in structure and bonding. CO2 is a linear molecule with carbon double-bonded to two oxygens. SO2 is a bent molecule with sulfur in a +4 oxidation state. SiO2 and TiO2 are oxide networks or lattice solids, where metals are coordinated to oxygen in three-dimensional frameworks. The physical state ranges from gases (CO2, SO2) to liquids and solids (SiO2, TiO2) depending on temperature and pressure. TiO2, for example, exists in several polymorphs, such as rutile and anatase, with differing optical and catalytic properties.

Formation and reactivity: dioxides are typically formed by oxidation of the element with oxygen, by thermal decomposition of related salts (like carbonates or sulfites), or as byproducts of combustion. In water, some dioxides act as acid anhydrides, forming corresponding acids; CO2 forms carbonic acid (H2CO3), while SO2 forms sulfurous acid (H2SO3). SiO2 and TiO2 are relatively inert under ordinary conditions but are important as structural materials and catalysts.

Uses and significance: CO2 is central to carbon cycling, used in beverages, enhanced oil recovery, and carbon capture. SiO2 is fundamental to glass, cement, and ceramics. TiO2 is a widely used white pigment and photocatalyst. Environmentally, dioxides play roles as greenhouse gases (notably CO2) and in industrial emissions, requiring monitoring and control. Safety considerations include respiratory effects from some gaseous dioxides and dust hazards from oxide powders.