A pure substance in chemistry is a form of matter that has a constant and definite chemical composition and consists of only one type of particle. This can be either a single element or a single compound, where all particles are identical and chemically combined. For example, pure water (H₂O) and table salt (NaCl) are pure substances because they contain only one type of molecule or formula unit throughout
. Key characteristics of pure substances include:
- Uniform composition throughout the sample.
- Particles are chemically bonded together.
- They have consistent chemical and physical properties.
- They cannot be separated into simpler substances by physical means.
- Examples of pure substances include elements like iron or gold, and compounds like water and carbon dioxide
In contrast, mixtures contain two or more different substances physically combined, with varying properties and compositions that can be separated by physical processes
. In summary, a pure substance is matter made up entirely of one kind of particle, with uniform composition and properties, distinguishing it from mixtures of different substances.
