compund

A chemical compound is a substance composed of two or more elements that are chemically bonded in a fixed, definite proportion. The combination forms a new material with properties that are typically different from those of its constituent elements. Compounds cannot be separated into their elements by physical means alone; their components must be broken apart through chemical reactions or other transformations.

Compounds are distinct from mixtures, where substances are physically combined and retain their own identities and can often be separated by physical methods such as filtration or distillation. In compounds, atoms are joined by chemical bonds and participate in reactions that rearrange bonds and produce new substances with specific stoichiometries.

Bonds that hold compounds together include ionic bonds, formed by electrostatic attraction between oppositely charged ions, and covalent bonds, formed by sharing electron pairs between atoms. Some materials historically described as alloys or intermetallics are also considered compounds when they have defined chemical formulas and compositions.

Representation of compounds is usually done with chemical formulas, which indicate the types and numbers of atoms in a molecule or formula unit. The empirical formula shows the simplest whole-number ratio, while the molecular formula indicates the actual numbers of atoms in a molecule. Examples include water (H2O), carbon dioxide (CO2), and sodium chloride (NaCl).

Compounds are central to chemistry, biology, medicine, and materials science. Their study includes synthesis, analysis, reactivity, and properties, along with naming conventions and structural descriptions that reflect their composition and arrangement of atoms.