Matter can be classified on the basis of its composition as element, compound or mixture.
All substances are made up of chemical elements. A chemical element is a basic form of matter that cannot be chemically broken down into simpler substances. A chemical element is a pure substance and it consists of one type of atom distinguished by its atomic number.
Examples of some elements are: helium, carbon, iron, gold, silver, copper, aluminum, hydrogen, oxygen, nitrogen, sulphur, copper, chlorine, iodine, uranium, and plutonium.
Elements are the building blocks of the Universe. In total, 114 elements have been listed so far. Out of the total 114 known elements, about 90 occur naturally on Earth and the remaining have been synthesized artificially by nuclear reactions. Only two elements namely hydrogen (92%) and helium (7%) make up about 99% of the total mass of the Universe. The remaining elements contribute only 1% to the total mass of the Universe.
Out of about 90 elements found naturally on Earth, two elements silicon and oxygen together make up almost three-quarters of the Earth’s crust.
A compound is a substance formed when two or more than two elements are chemically combined. A compound can be defined as a pure substance made from two or more elements chemically combined together in a definite proportion by mass. When elements join to form compounds they lose their individual properties.
Compounds have different properties from the elements they are made of. For example, water (a compound) is made up of elements - hydrogen and oxygen but properties of water are different from those of hydrogen and oxygen.
In everyday life we deal with a large number of substances but majority of them are not pure substances (elements or compounds). They are mixtures of two or more pure substances. There are two types of mixture depending on whether the parts of the mixtures completely mix or not - homogeneous mixtures and heterogeneous mixtures.