Chemical substances
Chemical Substances
Chemical substances (pronunciation: /ˈkɛmɪkəl ˈsʌbstəns/) are forms of matter with constant chemical composition and characteristic properties. They cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds.
Etymology
The term "chemical substance" is a combination of the words "chemical" and "substance". The word "chemical" originates from the Greek word "khēmeía" which means "alchemy", and the word "substance" comes from the Latin word "substantia", meaning "being, essence, material".
Related Terms
- Chemical compound: A chemical substance consisting of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition.
- Chemical element: A pure chemical substance consisting of a single type of atom distinguished by its atomic number.
- Chemical reaction: A process that leads to the transformation of one set of chemical substances to another.
- Chemical bond: A lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds.
- Chemical formula: A way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule.
Classification of Chemical Substances
Chemical substances can be classified into two broad categories: pure substances and mixtures. Pure substances include elements and compounds. Mixtures are a physical combination of two or more substances that can be separated by physical means.
Pure Substances
- Elements: An element is a pure substance that cannot be broken down into simpler substances by chemical means. Examples include hydrogen, oxygen, and nitrogen.
- Compounds: A compound is a pure substance composed of two or more different elements chemically combined in a fixed proportion. Examples include water (H2O), carbon dioxide (CO2), and sodium chloride (NaCl).
Mixtures
A mixture is a physical blend of two or more components, each of which retains its own identity and properties in the mixture. Examples of mixtures include air and salt water.
See Also
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