Compound: definition in chemistry
Compound: A substance made of two or more different elements chemically bonded in a fixed ratio, such as water (H₂O) or sodium chloride (NaCl).
A compound can have properties completely different from those of its elements: sodium is a reactive metal and chlorine a toxic gas, yet together they make table salt. Because the ratio of elements is fixed, every compound has a definite chemical formula. Compounds can only be broken down into their elements by chemical reactions, not by physical methods such as filtering.
Examples
- Water (H₂O) — two hydrogen atoms bonded to one oxygen atom
- Carbon dioxide (CO₂) — formed when fuels burn
- Sodium chloride (NaCl) — table salt
- Glucose (C₆H₁₂O₆) — a sugar made by plants
On the periodic table
Metals from the left side of the table combine with nonmetals from the right to form ionic compounds such as NaCl, while nonmetals combine with each other to form molecular compounds such as CO₂.