In this universe, everything is made of matter including the air we breathe, sand beneath our feet and the heavenly bodies.


States of Matter

The matter exists in four states such as solid, liquid, gas and plasma, however we consider only three states of solid, liquid and gas for our regular study. Substances made of matter take any of these four forms, but adding or removing energy could readily change the state. For example when heat energy is removed from water (liquid state), it becomes ice (solid state) and when heat energy is added to water it becomes steam (gaseous state).

Solid: Solid materials are formed from densely packed particles called molecules. These molecules are greatly attracted to each other and held together in an order. Molecules do not move around freely in solids but vibrate in their position. With increase in temperature, these molecules vibrate faster and gain kinetic energy. Solid particles expand very little when heated but not as much as liquids and gases do.

Liquid: Materials in a liquid state have definite volume at a given temperature, but do not confirm to definite shape. Molecules in liquid substances move rapidly in all directions and frequently collide with each other. With increase in temperature, the molecules move faster and gain kinetic energy. Liquids expand when heated and contract when cooled. They flow freely but not as fluid as gases. Liquids are not compressible.

Gas: Materials in a gaseous state have molecules widely spread and scattered across its container. In gases, the molecules move more freely in all directions and frequently collide with each other and the walls of the container. When heated, the molecules move faster and gain kinetic energy. They also expand on heating and contract on cooling. However they have no surface, fixed shape or volume. Gases are highly compressible.


Phase Changes of Matter

Matter can change from one state/phase to another at a specific temperature and surrounding pressure. However, the temperature is the determining factor in material’s phase change because pressure is typically the atmospheric pressure.

        When heat is applied to a solid matter, it changes its state and goes from solid to liquid to gas. There are some exceptions where the matter will go directly from a solid to a gas.

        When a gas is cooled, it changes its state and transits from gas to liquid to solid. There are some exceptions where the material will go directly from a gas to a solid.


Types of Phase Changes


Melting: Melting is a phase transition in which a solid substance changes into liquid substance. When heated, the temperature of the particles in solid matter rises. As the temperature rises, the particles vibrate very rapidly and gain kinetic energy. Once the temperature reaches to a melting point, the internal ordered structure of the particles break and solid starts to melt into liquid. Each material has a set melting point at normal air pressure. Thus at high altitudes where the pressure is low, the melting point also low.

Freezing or Solidification: Freezing is a phase transition in which a liquid substance turns into a solid substance. When a substance is cooled, the particles release temperature. Once the temperature drops to its freezing point the liquid turns into solid. For example, red hot lava in liquid form erupts and turns into solid rock once it meets the earth’s surface.

Boiling or Vaporization: When liquid is heated, the particles gain kinetic energy and move faster and further apart. At a boiling point, the particles break free of one another and the liquid turns to gas. The boiling point of a substance is always the same.

Condensation: A phase transition in which gas turns into liquid is called condensation. As the temperature drops, the water vapour turns into liquid water droplets due to condensation.

Evaporation: Evaporation is a phase change in which liquid turns into gas below its boiling point. This occurs when some particles in a liquid that have enough energy break free from the rest to become a gas.



The elements are the fundamental substances of all matter, which cannot be broken down by any physical or chemical means. Elements may exist in the form of atoms or molecules.

        As of April 2011, scientists have discovered or created 118 elements. All the elements are arranged according to their atomic number on a chart called Periodic Table of Elements. First 92 elements (Hydrogen, Helium, gold, silver, carbon and so on) listed in the periodic table were found in nature and the rest (Dubnium, Fermium and so on) were created in laboratories. Some elements such as hydrogen, oxygen, carbon and nitrogen make up the living organisms.

        A particular element will have only one kind of atom and the number of protons in that atom defines the type of element. For example, an atom having 6 protons, 6 neutrons and 6 electrons will always make up an element called carbon and carry the same properties of that carbon element, whereas an atom having 1 proton and 1 electron will always make up an element called hydrogen and carry the same properties of hydrogen element.