Look around your classroom. What do you see? You might see
your bench, table, blackboard, window etc. What are these things made of ? They
are all made of matter. Matter is defined as anything that has mass and
occupies space. All matter is composed of atoms. This knowledge of matter is
useful to explain the experiences that we have with our surroundings. In order
to understand the properties of matter better, we need to classify them. There
are different ways to classify matter. The two most commonly used methods are
classification by their physical state and by chemical composition as described
in the chart
Matter can be classified as solids, liquids and gases
based on their physical state. The physical state of matter can be converted
into one another by modifying the temperature and pressure suitably.
Matter can be classified into mixtures and pure substances
based on chemical compositions. Mixtures consist of more than one chemical
entity present without any chemical interactions. They can be further classified
as homogeneous or heterogeneous mixtures based on their physical appearance.
Pure substances are composed of simple atoms or molecules.
They are further classified as elements and compounds.
An element consists of only one type of atom. We know that
an atom is the smallest electrically neutral particle, being made up of
fundamental particles, namely electrons, protons and neutrons.
Element can exist as monatomic or polyatomic units. The
polyatomic elements are called molecules.
Example : Monatomic
unit - Gold (Au), Copper (Cu); Polyatomic
unit - Hydrogen (H2), Phosphorous (P4) and Sulphur (S8)
Compounds are made up of molecules which contain two or
more atoms of different elements.
Example : Carbon dioxide (CO2), Glucose (C6H12O6),
Hydrogen Sulphide (H2S), Sodium Chloride (NaCl)
Properties of compounds are different from those of their
constituent elements. For example, sodium is a shiny metal, and chlorine is an
irritating gas. But the compound formed from these two elements, sodium
chloride, shows different characteristics as it is a crystalline solid, vital
for biological functions
By applying the knowledge of chemical classification,
classify each of the following into elements, compounds or mixtures.