If we look around us we find many substances such as pencil box, pen, air, water, etc. All these things have two things in common and that is they occupy space and have mass. These things are known as matter.

Matter is made up of particles. The characteristics of particles of matter are as follows:

  • The size of particles is tiny.
  • The particles of matter have spaces between them. This is referred to as intermolecular space (IMS).
  • The particles of matter have forces of attraction between them. This is referred to as intermolecular force (IMF).
  • The particles of matter are continuously moving. The energy  by which particles move is known as kinetic energy(K.E.)

In bulk, the matter can exist in different forms or states of aggregation known as phases. These phases depend on ambient pressure, temperature and volume. These phases include solid, liquid, gas, plasma, and Bose-Einstein Condensate.

The phases are sometimes referred to as states of matter. However, this can lead to confusion . For example, two gases maintained at different pressure are in different states but in the same phases.

On basis of intermolecular space and intermolecular forces of attraction among the particles, initially, the matter was broadly classified into 3 states of matter.

SOLID STATE: The particles in solid-state have fixed positions and can oscillate about their mean positions. This makes the solid rigid in nature. The intermolecular forces among the molecules tend to keep the molecules closer, whereas thermal energy tends to keep them apart by making them move faster. At sufficiently lower temperatures, the thermal energy is low and forces bring them so close that they cling to one another and occupy fixed positions. These can still oscillate about their mean positions and the substance hence exist in a solid-state.

On the basis of the nature of order present in the arrangement of their constituent particles, solids can be classified as crystalline or amorphous.

A crystalline solid usually consists of a large number of small crystals, each of them having a definite characteristic geometrical shape. It has long-range order which means that there is a regular pattern of arrangement of particles that repeats itself periodically over the entire crystal. These solids have a sharp melting point and are anisotropic in nature, that is, some of their physical properties like electrical resistance or refractive index show different values when measured along with different directions in the same crystals. This arises from the different arrangements of particles in different directions. Example: Sodium chloride and quartz

An amorphous solid (Greek amorphos = no form) consists of particles of irregular shape. The arrangement of constituent particles in such a solid has only short-range order. In such an arrangement, a regular and periodically repeating pattern is observed over short distances only. Such portions are scattered and in between the arrangement is disordered. The structure of amorphous solids is similar to that of liquids. Like liquids, these solids have a tendency to flow, though very slowly. Therefore, sometimes these are called pseudo solids or supercooled liquids. These solids soften over a range of temperatures and can be molded and blown into various shapes. On heating, they become crystalline at some temperature. Amorphous solids are isotropic in nature. It is because there is no long-range order in them and arrangement is irregular along with all the directions. Therefore, the value of any physical property would be the same in any direction.

Example: Glass, rubber and plastics

LIQUID STATE: It is the state of matter in which intermolecular forces (Van der Waals Forces) are stronger than in a gaseous state. Because molecules do not separate from each other, therefore the liquids have a definite volume. Since the molecules of liquids can move past one another freely, therefore, liquids can flow and hence is said to possess fluidity. The liquids have translational motion i.e. liquids move as a whole (the molecules can slide over each other but they cannot break away from the intermolecular forces while in the liquid state.)Examples: milk, alcohol, water, etc.

Water is considered to be a wonder liquid. This is so because it supports many life forms which have been possible because of the presence of dissolved oxygen in it. Hence, we can say the rate of diffusion of gas in a liquid is higher.

GASEOUS STATE: It is the state of matter in which neither the volume nor the shape is fixed i.e. they take the shape of the container in which it is kept. The particles of the gaseous state are highly compressive in nature. Due to this property, the large volumes of gas can be compressed into a small cylinder and can be transported easily. Example: CNG (Compressed Natural Gas) is used as fuel in vehicles.

The particles of gas move randomly in all directions with high Kinetic energy. Because of this random movement, the particles may hit each other and also the walls of the container. Hence, the large pressure is exerted on the walls of the container.

The behavior of gaseous particles is governed by some general laws which have been discovered experimentally. These laws are based on certain assumptions which form the basis of the Kinetic Theory of gases. These laws include Boyle’s law, Charles’ Law, Avogadro Law, and Gay-Lussac’s Law. The gases which obey all these laws are said to be ideal gas and the gases which do not obey are said to be real gases. In reality, no gas is an ideal gas. All gases are real gases. However, at very low temperatures and high pressure, the real gases can behave like ideal gas.

Hence, we can differentiate between solid, liquid and gas in tabular form:

1.Pictorial representation
2.Packing of particlesTightly packedNeither so tight nor so looseLoosely packed
3.Inter molecular spaceVery lessmoderatemaximum
4.Inter molecular forcemaximummoderateminimum
5.Kinetic Energy of particlesminimummoderatemaximum
7.RigiditymaximumNo rigidityNo rigidity
9.VolumefixedfixedNot fixed
10.FluidityNo fluidityFluidity observedMaximum fluidity observed.

 Later on, scientists started talking of 5 states of matter: Solid, Liquid, Gas, Plasma, and Bose-Einstein Condensate.

PLASMA STATE: It is the fourth state of matter. It was first discovered by Sir William Crookes in 1879. The super energetic and super excited particles encompass this state. In this, the particles are in the form of ionized gases consisting of positive ions and free electrons.

It is created by adding energy to a gas so that some of the electrons leave its atom. This process is called ionization. Since the particles of this state of matter have high energy; therefore the particles in the plasma will react strongly to electric and magnetic fields.

Plasma is usually very hot because it takes very high temperatures to break the bonds between electrons and nuclei of atoms. Plasma can have very high pressure as in stars or very low pressure in outer space.

It is believed that over 99% of the matter in visible universe is plasma. Since all states of matter indirectly arise from this, therefore it should be considered as first state of matter and not the fourth state.

On Earth, the natural phenomena of lightning create a plasma state. However, its artificial uses include fluorescent light bulbs, neon signals, plasma lamps, etc.

BOSE –EINSTEIN CONDENSATE: Satyendra Nath Bose in 1920 had done some calculations for fifth state of matter. On the basis of is calculations, Albert Einstein predicted a new state of matter-the Bose Einstein Condensate (BEC).

It is the state of matter which is formed by the cooling of gas of extremely low density. They are effectively super atoms, a group of atoms that behave as one. They have very low energy. It is formed by cooling a gas of extremely low density.

BECs are more ordered than solids in that their restriction not only occurs at molecular level but also at atomic levels. Atoms in BEC are locked into all of the same attributes as each other, that they are literally indistinguishable. When BEC is visible, each part that one can see is the sum of the portion of each atom all behaving in same way rather than being the sum of atoms as in other phases of matter.

The most common known property of BEC is their superfluidity i.e. BECs flow without interior friction. Since they are effectively super atoms, BECs are all moving in a similar way at the same time when they flow and don’t have energy losses due to friction.

Hence, in comparison, we can say that the energy of BECs is minimum while that of the plasma is the maximum.

The five states of matter are interconvertible. On the application of pressure and temperature, one state of matter can be changed into another. On increasing the pressure, the particles of matter come close to each other, and hence their energy decreases while on increasing the temperature the particles of matter move away from each other, and the thermal energy of constituent particles increases.

The interconversion of 4 states of matter can be shown as follows:

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