Matter is the stuff everything you see around yourself is made of. For years, scientists have devoted themselves to studying properties of matter in all its manifestations. This quest ultimately led to the discovery of the building blocks of matter which are atoms and molecules. A molecule is a union of one or more atoms. There are 92 naturally occurring types of atoms that can combine together in various ways to create zillions of different types of molecules, which further combine to create mixtures of various kinds. Thus, atoms combine in various ways with each other to create the complex world that you see around yourself.
What is a Pure Substance?
It is something which cannot be divided into parts, as it's all made up of the same thing. Everything is made up of 92 different types of atomic elements, which cannot be divided further. Therefore, atoms are the purest substances. For example, Hydrogen gas is a pure substance, as it is made up of only Hydrogen atoms or molecules. Carbon, gold, phosphorous are some more examples of elements. These atoms can combine to form compounds, which are also pure substances, as they cannot be physically divided into their constituent atoms. Examples are distilled water (H2O) and pure common salt (Sodium Chloride).
What is a Mixture?
Mixtures are a random potpourri, containing various types of substances, which haven't chemically reacted with each other. It is created through a physical assortment of pure substances brought together. It can be homogeneous (of uniform composition) or inhomogeneous (of nonuniform composition). Saltwater is an example, where various substances including salts are mixed together.
Differences Between Pure Substances and Mixtures
The prime difference lies in the fact that the pure substances cannot be divided into constituents while the mixtures can be. The separation of a mixture into its constituent parts is carried out using physical techniques like distillation, filtering and particle separation, but a pure substance, like any compound, can be rarely separated into constituent atoms by physical methods. Chemical reaction must occur to separate a compound into its constituent parts.
Unlike mixtures, which have no fixed proportion in which constituent elements mix, compounds are created from the combination of atoms in specific proportions. As no chemical reactions occur between the substances forming a mixture, each one of them retains their chemical properties. On the other hand, in a compound, the individual properties of constituent atoms are lost, as they chemically react with each other to create a compound, which may have entirely different properties.
Remember that pure substances are compounds and elements (made up of the same atom or same molecule respectively), while mixtures are an assortment of different substances put together. The former are rarely found naturally, while the world is replete with mixtures of all kinds. Refineries and chemical labs devise various physical and chemical techniques to separate a mixture into its individual components.