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States of matter


What is matter?

Matter is anything that has mass and occupies space. It includes things that can be seen (all living and non-living, natural and synthetic things) and cannot be seen to the naked eye (e.g. air and microorganisms).

Physical states of matter

Matter exists in three physical states: solid, liquid and gas.


The particles in a solid are packed tightly with a regular pattern. Hence, they do not pass each other. Solids have a fixed shape and a fixed volume.


The particles in a liquid are situated close together without a regular pattern. The distance between two particles is large enough for one particle to pass the other. Liquid takes the shape of the container - it has an indefinite shape. Liquid has a fixed volume.


The particles in a gas are separated without a regular pattern. Gas takes the shape of the container - it has an indefinite shape. Gas fills the space of the container - it has an indefinite volume. 

Atoms in a solid mass
Atoms in a liquid
Atoms in a gas

Change of state

The conversion of a substance from one state to another is known as the change of state.


  • Melting of ice (solid to liquid).
  • Boiling of water (liquid to gas).
  • Freezing of water (liquid to solid).

Water is one of the few substances which can exist in all three states: solid ice, liquid water, gaseous steam. State changes have different names depending on which states are involved:

  • The change of solid to liquid is known as melting.
  • The change of liquid to gas is known as vaporization.
  • The change of gas to solid is known as deposition.
  • The change of solid to gas is known as sublimation.
  • The change of liquid to solid is known as freezing.
  • The change of gas to liquid is known as condensation.

Diagram of changing states of matter from liquid to gas to solid and vice versa

Properties of matter

Properties of matter can be classified into two types depending on whether the particular property is determined by changing the chemical identity or composition of the substance.

Properties of matter
Are the properties observed/measured without changing the chemical identity of the substance?
NO = chemical property
YES = physical property
Flammability - when wood burns it changes to ashes Shape

Corrosion - rusting of iron objects after exposure to moist air for a long time

Decomposition - hydrogen peroxide decomposes into water and oxygen in the presence of heat or light Odour
Reactivity - potassium reacts with water Hardness
  Melting point

Boiling point

  Physical state (liquid, solid, gas)

Changes in the matter

Changes in the matter are classified into two categories: physical change and chemical change.

Physical change

A physical change is when the substance changes its physical appearance or state without affecting the chemical identity. For example, the melting of ice to give water is a physical change because water only changes its physical state from solid to liquid without affecting its chemical identity. 


  • the grating of a piece of cheese
  • boiling of water
  • sugar dissolving in water

Chemical change

A chemical change is a process in which the substance changes its chemical identity or composition. It involves the formation of new substances that have different properties compared to the original substance. For example, iron objects turn reddish-brown (known as rusting) when exposed to moist air for a long period is a chemical change because iron combines with oxygen and moisture from the air to form a new substance, rust.


  • sugar heated in a saucepan to make caramel
  • burning of potassium in water
  • milk turning sour

Classification of matter

The flowchart below shows how you can determine the classification of matter through a series of simple yes/no questions. 

Classification of matter


Anything that has mass and occupies space
Are properties and composition constant?


Pure substance

A substance that has a uniform chemical composition throughout
e.g. Water, sugar, table salt
Can the pure substance be broken into simpler substances?


Chemical compound

Can be chemically broken down into constituent elements e.g. Water, sugar, table salt


Cannot be broken down into simpler substances by chemical or physical means e.g. Hydrogen, oxygen, sulphur


Physical combination of two or more pure substances
e.g. Salt-sand mixture, sea water, concrete
Does the mixture have a uniform composition throughout?


Homogenous Mixture

One visible phase which has uniform composition throughout e.g. Sea water, coffee, air

Hetereogeneous mixture

Two or more visible phases which have non-uniform composition throughout e.g. Vegetable stew, meat pie

Test your knowledge

Take the States of matter: Quiz

Use the States of Matter: Interactive

States of Matter: Basics