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Chemical compounds are made up of two or more elements that bond in a fixed ratio, determining their physical and chemical properties. They are represented by formulas, with more complex compounds requiring more complex formulas. Compounds differ from mixtures in their properties and require a chemical reaction to create. They can exist in different phases and are monitored by the CAS registry.
Chemical compounds are a substance made up of two or more related elements. Elements bond in a fixed ratio to create a particular compound. The ratio and types of elements that compose it determine its physical and chemical properties. By combining to form compounds, elements become more stable.
Chemists represent chemical compounds using a variety of formulas that describe the types of elements that make them up. For example, in a molecular formula, the elements that make up the compound are listed, including the ratio in which each element appears. “Na,” which is the elemental symbol for sodium, and “Cl,” which is the elemental symbol for chlorine, combine to form “NaCl,” which stands for sodium chloride or table salt.
More complex compounds require a more complex formula. For example, water is represented by H2O, which means two parts hydrogen to one part oxygen. Other formulas reveal some of the structural information for compounds.
Chemical compounds differ from simple mixtures of elements in their physical and chemical properties. The properties of a mixture are most similar to the elements that make up the mixture, but the properties of a compound rarely mimic the contributing elements because a chemical reaction must take place, resulting in a chemical change, to create a compound. Once a compound is created, breaking it down often requires the addition of energy, such as heat, while breaking down mixtures often only requires a simple filtering process. Some substances exhibit the properties of both compounds and mixtures.
Similar to elements, chemical compounds can exist in different phases. The solid is the most common, although some compounds are only in the solid phase at extremely low temperatures. Depending on temperature and pressure, some can also exist as liquids, gases and plasmas. When heat is applied, they typically begin to decompose into smaller compounds or individual elements.
Every chemical compound is monitored by the American Chemical Society’s Chemical Abstracts Service, sometimes called CAS. Compounds receive a unique identification number, called a CAS registry number. CAS tracks tens of millions of unique substances, and thousands of new ones are added every day. The development of the registry dates back to 1957.
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