What is the Meaning & 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 that which presents a stable chemical composition, such as water, helium, nitrogen or carbon dioxide. However, the absolute purity does not exist, since we live in a world in which all natural substances are somehow blends, which can be separated in their pure components until the desired degree of purity.
From a commercial point of view, a pure substance can have between 90 and 99% purity. In the heavy industry the purest substance which is used is the water big lines of steam, which can reach a 99, 99% purity.
A pure substance doesn't have to necessarily be a single element or chemical compound is a mixture of different chemical elements also a pure substance, provided that the mixture is homogeneous.
It must be borne in mind that molecules that make up matter are made, in turn, of atoms linked together. There are millions of different molecules, some are of industrial type and others are part of nature. However, the atoms that form molecules are not infinite, but that there are 118 different atoms (which are established in the periodic table of the elements).

Phases of the pure substances and their classification

Pure substances can occur at different stages. A phase is a State of a substance that may present possible changes of State, as for example the different phases (solid, liquid and gaseous) water. In this sense, should take into account that each substance has a series of particular physical properties (density, boiling or melting point).
Pure substances are classified into two groups: elements or simple substances and, on the other hand, composite elements. The first may not decompose in other simpler since they consist of a single class of atoms (for example, a sheet of copper is formed by atoms of the metal or all the elements of the periodic table). Composite substances are a type of matter consisting of two or more different elements and which are chemically attached in a definite proportion (for example, sodium chloride)
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