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. Â 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.Â
Example of Compounds:Â 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.Â
Mixture is of two types:Â Homogeneous and heterogeneous. Â Homogeneous mixtures have the same composition
throughout. Heterogeneous mixtures have different composition in different
parts of the mixture.
Example of Mixtures:Â 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.