definition of pure substances

Matter is everything that exists in the universe as a whole. Matter can be divided into two types: pure substances and mixtures. A pure substance is one that has a stable chemical composition, such as water, helium, nitrogen, or carbon dioxide. However, absolute purity does not exist, since we live in a world in which all natural substances are in some way mixtures, which can be separated into their pure components to the desired degree of purity.

From a commercial point of view a pure substance can be between 90 and 99% pure. In heavy industry the purest substance used is water from large steam pipes, which can reach 99.99% purity.

A pure substance does not necessarily have to be of a single element or chemical compound but a mixture of different chemical elements is also a pure substance, as long as the mixture is homogeneous.

It must be borne in mind that the molecules that make up matter are made, in turn, of atoms bound together. There are millions of different molecules, some are industrial and others are part of nature. However, the atoms that make up the molecules are not infinite, but there are 118 different atoms (those that are established in the periodic table of the elements).

The phases of pure substances and their classification

Pure substances can occur in different phases. A phase is a state of a substance that can present possible changes of state, such as the different phases of water (solid, liquid and gas). In this sense, it must be taken into account that each substance has a series of particular physical properties (density, boiling point or melting point).

Pure substances are classified into two groups: simple elements or substances and, on the other hand, compound elements. The former cannot be decomposed into simpler ones because they are made up of a single class of atoms (for example, a copper sheet is made up of atoms of this metal or all the elements of the periodic table). Compound substances are a type of matter made up of two or more different elements that are chemically united in a defined proportion (for example, sodium chloride)

Photos: iStock - Srdjana1 / Borut Trdina

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