substancecompounds

Substance compounds, commonly referred to as chemical compounds, are pure substances composed of two or more elements bound together by chemical bonds in definite, fixed ratios. The chemical formula of a compound expresses the proportion of each element, and the compound’s properties—such as melting and boiling points, density, and reactivity—are typically distinct from those of its constituent elements.

Compounds differ from mixtures in that their components are chemically bonded and cannot be separated by simple physical methods. Most compounds form when elements combine in a chemical reaction, yielding substances with a fixed composition. Compounds can be solids, liquids, or gases, and they may crystallize into regular lattices or exist as discrete molecules.

Classification often follows the type of chemical bonding. Ionic compounds form through electrostatic attraction between positively and negatively charged ions, as in sodium chloride (NaCl). Covalent or molecular compounds consist of atoms held together by shared electron pairs, such as water (H2O) and carbon dioxide (CO2). Some substances form extended networks, such as silicon dioxide (SiO2).

Naming and representation rely on established conventions. Compounds are given systematic names or common names, and their formulas denote the number of atoms of each element. IUPAC rules guide nomenclature, while formulas reflect the compound’s composition and structure. Substance compounds play central roles across chemistry, biology, medicine, and materials science.