Chemical
Classifications
Substances

The number of known substances in the world is about 20 million and continues to grow exponentially. New compounds are identified and synthesized in the laboratory at such a rate that chemists expect there will be nearly 5 billion substances by 2100. Fortunately, many of these substances share properties that can be used to classify them into a smaller number of groups. But, what is it that chemists call a "substance"?

From the chemical point of view, a substance is a type of matter that has specific physical and chemical properties, and a fixed composition. Pure water is a typical example. It always boils at 100 oC at atmospheric pressure, and it is composed by hydrogen and oxygen in a definite proportion. Sugar, carbon, ethanol, oxygen, and gold are other examples of substances.

In ChemThreads, the word "substance" is always used to denote a "pure substance".




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