Basic Definitions


Anything that has mass and occupies space is called matter.


Water, wood, air, paper, gold etc.

Classification of Matter

All materials are either a substance or a mixture. The following figure shows simple classification of the matter into different forms.

Classification of Matter



It is a matter that has a particular set of characteristics which differ from the character of any other kind of matter.


Oxygen, water, urea, glucose and common salt are different substances.


i.It is formed by a chemical combination of atoms of the elements.Mixture is formed by the simple mixing up of the substances.
ii.The constituents lose their identity and form a new substance having entirely different properties from them.Mixture shows the properties of the constituents.
iii.Compounds always have fixed composition by mass.Mixtures do not have fixed composition.
iv.The components cannot be separated by physical means.The components can be separated by simple physical methods.
‘ V.Every compound is represented by a chemical formula.It consists of two or more components and does not have any chemical formula.
vi.Compounds have homogeneous composition.They may be homogeneous or heterogeneous in composition
vii.Compounds have sharp and fixed melting points,Mixture does not have sharp and fixed melting points.

The substance that cannot be converted into other simpler substances is called an element.

Oxygen, hydrogen, Iron, copper and gold are few examples of elements.

Modern definition of Element

It is a substance made up of same type of atoms, having same atomic number. Compound

A compound is a pure substance that is made up of two or more elements held together in fixed ratios by natural forces called chemical bonds.

The properties of compounds are different from the properties of the elements from which they are formed. Elements and compounds have uniformed composition throughout.


Water, carbon dioxide, copper sulphate, sodium chloride etc. are compounds.


An impure substance that contains two or more pure substances which retain their individual chemical characteristics is called a mixture.

The entire world is made up of mixture of element and compound. A mixture can be converted into two or more pure substances by a physical method.


Air, water containing dissolved oxygen, table salt dissolved in water, salt and etc..Types of Mixture

  1. a) Homogenous Mixture

A mixture that consists of only one phase is called homogenous mixture.


Salt or sugar dissolved in water, air etc Homogenous mixtures have uniformed composition throughout.

  1. b) Heterogeneous Mixture

A mixture that consists of two or more visibly different components is called heterogeneous mixture.


Sand + Salt, oil floating on water, a class room etc.



The following are important differences between a compound and a mixture

Table Difference between a Compound and a Mixture

Atomic Number

The number of protons in the nucleus of an atom is known as its atomic number.

It is represented by symbol “Z”. As all atoms of an element have same number of protons in their nucleus, they have same atomic number.


All hydrogen atoms have 1 proton, their atomic number is 1. Similarly all atoms in carbon have 6 protons, their atomic number is 6.

 Mass Number

The total number of protons and neutrons is an atom in known as its mass number. It is represented by symbol ‘A’.


Hydrogen atom has one proton and no neutron in its nucleus hence its mass number is 1. Carbon atom has 6 protons and 6 neutrons; hence its mass number is 12.

The difference between the mass number and the atomic number is equal to the number of neutrons in the nucleus

No of neutron = Mass number – Atomic number

= A – Z

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