Compound
Definition and meaning of Compound in chemistry.
Compound is a pure substance made when two or more different elements join together in a fixed ratio through chemical bonds. The atoms cannot be separated by simple physical methods like filtering or evaporation. Only a chemical reaction can break a compound back down into its elements.
In more detail
Chemists sort compounds into two main types based on how the atoms bond. Ionic compounds form when a metal transfers electrons to a nonmetal, creating charged particles called ions that attract each other. Covalent compounds form when two nonmetals share electrons instead of trading them.
Because the atoms are locked into a specific ratio, every pure sample of a compound has identical composition. This rule is called the law of constant proportions. Chemical formulas like H2O or NaCl show the exact ratio of atoms in a compound.
A compound's properties are usually very different from the properties of the elements that formed it. Table salt is a stable white solid, but it forms from sodium, a soft reactive metal, and chlorine, a toxic green gas. Students often confuse compounds with mixtures.
A mixture, like salt water, keeps the properties of its parts and can be separated by physical means such as evaporation. Ionic compounds are usually named with the cation first, such as sodium chloride, while molecular compounds often use prefixes like mono, di, and tri to show atom counts, as in carbon dioxide, CO2.
Key facts
| Formula example | H2O (water) |
|---|---|
| Bond types | Ionic or covalent |
| Composition rule | Fixed ratio by mass (law of constant proportions) |
| Separation method | Only by chemical reaction, not physical methods |
| Field | General Chemistry |
Water, H2O, is a compound in which two hydrogen atoms bond covalently to one oxygen atom. Hydrogen and oxygen are both gases at room temperature, but water is a liquid with completely different chemical behavior. This shows how bonding creates a substance with its own unique identity. Similarly, carbon dioxide, CO2, is a compound of carbon and oxygen that behaves nothing like either pure carbon or pure oxygen gas.
Frequently asked questions
What is the difference between a compound and a mixture?
A compound's atoms are chemically bonded in a fixed ratio and need a chemical reaction to separate. A mixture's parts are only physically combined, can vary in proportion, and can be separated by physical methods like filtering.
Is table salt a compound?
Yes. Sodium chloride, NaCl, is an ionic compound formed when sodium and chlorine atoms combine in a 1 to 1 ratio.
Can a compound be broken back into its elements?
Yes, but only through a chemical reaction. Electrolysis of water, for example, splits H2O back into hydrogen gas and oxygen gas.