Chemical compound

Composition and bonding

The atoms in a compound may be arranged as discrete molecules, as in many gases and liquids, or as extended networks without separate molecules. For example, every water molecule contains one oxygen and two hydrogen atoms, whereas common salt (sodium chloride) forms an extended lattice of alternating sodium and chlorine ions. Bonding types—ionic, covalent, metallic, and hydrogen bonding—determine structure and many physical properties.

Physical forms and common examples

Compounds occur as solids, liquids, or gases depending on their intermolecular forces and temperature. Typical examples include water (a liquid at ordinary conditions), sodium chloride (a crystalline solid), and carbon dioxide (a gas at room temperature). Their melting point, boiling point, electrical conductivity, solubility, and hardness reflect internal bonding and structure.

Origins, synthesis and history

Compounds are found in nature—many are produced by plants, animals and geological processes—or they can be made in laboratories and industrial facilities. The idea that compounds contain elements in fixed proportions helped shape modern chemistry: historically, the law of definite proportions and early atomic theories showed that compounds are built from atoms combined in reproducible ratios.

Uses, reactions and safety

Compounds are central to industry, medicine, agriculture and research. They are transformed by chemical reactions to make fuels, polymers, pharmaceuticals and many consumer goods. While many compounds are benign, some are hazardous: certain chemicals are poisonous, corrosive, flammable or explosive. Trained scientists and technicians use protocols and protective equipment to handle them safely; workers in factories that process chemicals commonly follow strict regulations and wear protective clothing.

Types and important distinctions

• Molecular compounds: Composed of molecules with covalent bonds (e.g., water).
• Ionic compounds: Formed from positive and negative ions in an extended lattice (e.g., sodium chloride).
• Metallic compounds/alloys: Metals sharing delocalized electrons; often conductive and malleable.
• Covalent network compounds: Large networks of covalently bonded atoms that form very hard solids (e.g., diamond).

It is important to distinguish compounds from elements (single kinds of atoms) and mixtures (physical blends that retain separate identities). A compound can be broken into simpler substances only by chemical means, not by physical separation. For further basic definitions and examples, see introductory chemistry resources linked above.