Based on the chemical composition of the substance, matter may be classified as elements, compounds or mixtures.
a) Elements: These are substances which cannot be reduced to simpler materials either by physical or chemical changes. At present 118 different elements are known. About 92% of the elements can be extracted from natural sources but the rest are prepared from artificially by means of nuclear processes. Elements are represented by Symbols.
Example of elements: Copper (Cu), Oxygen (O), Hydrogen (H), helium (He), Lithium (Li)
b) Compound: A compound is a substance which contains two or more elements chemically combined together. Water is made up of hydrogen and oxygen atoms. Carbon dioxide is up of carbon and oxygen. Unlike elements , compounds can be decomposed, or broken down by simple chemical reactions.
Example of Compounds: Water (H2O), Salt (NaCl), Ammonia (NH3), Methane(CH4), Benzene (C6H6). Sugar(CHO)n, Sulphuric acid (H2SO4), Marble, Saltpetre
c)Mixture: When two or more substances are combined by physical methods in any proportion and no new substances is formed then it is called a mixture.
Mixture is of two types: Homogeneous and heterogeneous. Homogeneous mixtures have the same composition throughout. Heterogeneous mixtures have different composition in different parts of the mixture.
Example of Mixtures: Sand, Air is mixture of gases, Sugar and water, Combination of sulphur, iron fillings. The constituents of a mixture can be separated by ordinary physical methods.