Pure Substances – The constituents of mixture can not be separated by simple physical methods.
(i) Elements – Substance that cannot be decomposed into two or more different substances by a simple chemical process.
e.g. hydrogen, oxygen
(ii) Compounds – Substance of definite composition that can be decomposed into two or more different substances by a simple chemical process.
• The properties of all substances and elements obtained on decomposition of the compounds are completely different.
e.g. water composed of two atoms of hydrogen and one atom of oxygen. On decomposition, it gives hydrogen and oxygen which have completely different properties than water.