Matter exists in three different states solid, liquid and gas. These states of matter arise due to the variation in the extent of intermolecular forces and intermolecular space.

The Solid State

In this state of matter, the substances have definite mass, volume, and shape. Wood, table, pen, and book are examples of solid states of matter. The intermolecular space in between the constituent particles of solid state is small, but the intermolecular forces are strong. Thus, the constituent particles such as atoms, molecules or ions cannot move but can only oscillate about their mean position. This is the reason why solids are incompressible and rigid i.e., have definite shape and size. Because of the presence of strong intermolecular forces, these are highly dense and generally have high melting point.

Classification of Solids

These can be classified into two groups

1. Crystalline Solids. They consist of a large number of crystals. In a crystal, the arrangement of particles is regular e.g., sodium chloride, diamond, quartz (crystalline), graphite, etc.
2. Amorphous Solids They consist of particles of irregular shape. The arrangement of particles in amorphous solid is disordered, e.g., glass, rubber, and plastics, amorphous solids are also called pseudo solids or supercooled liquids.

The Liquid State

In this state, the substances have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept, e.g., water, oil, milk, etc. The upper surface of the liquid is always planar whatever be the shape of the container. Liquids flow and change their shape, so they are not rigid and are called fluids ( the substance which can flow). In liquids, intermolecular forces are no longer strong enough to hold the particles together, that’s why they are less densely compressed. However, the forces are still sufficient so that particles cannot escape each other’s environment, so they have sufficient mobility and fixed volume.

The Gaseous State

In this state, matter has no fixed shape and volume. They only occupy the shape and size of the container in which they are kept e.g., air, H2, O2, N2, etc. In the gaseous state, the intermolecular forces are very weak, so the intermolecular spaces between the molecules are very large. This is the reason that gases are highly compressible as compared to solids and liquids. Gases also flow in the container as compared to solids and liquids. Gases also flow in the container in which they are kept so they are also called fluids. Further, gases expand more as compared to liquids and solids when heated due to the weaker intermolecular forces as compared to liquids and solids

Plasma State

It consists of super energetic and super excited particles. These particles are in the form of ionized gases. The fluorescent tube (filled with helium or any other gas) and neon sign bulbs (filled with neon) consist of plasma. The sun and the stars glow because of the presence of plasma in them. The plasma is created in stars because of very high temperature.

Bose-Einstein Condensate (BEC)

This state of matter is named after the name of scientists Satyends Nath bose (India) and Albert Einstein. The BEC is formed by cooling a gas of extremely low density, about one hundred thousandths the density of normal air, to super low temperatures. In 2001, Eric A Cornell, Wolfgang Ketterle and Carl E Wieman of USA received nobel prize in Physics of achieving (Bose-Einstein Condensate)

The state of matter is interconvertible. They can be interchanged by changing temperature or pressure as Various terms related to interconversion of states of matter are

1. Fusion The process of melting, i.e., change of solid state into a liquid state is also known as fusion.
2. Melting Point The temperature at which a solid starts to melt to become a liquid at the atmospheric pressure is called its melting point. The melting point of a solid is an indication of the strength of the force of attraction between its particles i.e., higher the melting point of solid, higher will be the force of attraction between the particles of solid. Melting point of ice is 0ºC
3. Sublimation It is the process used for those solids which convert directly into vapors on heating without converting into a liquid phase and the vapors upon cooling give back the solid. Such solids are called sublimates.
4. Vaporisation The process in which a liquid substance changes into a gas rapidly on heating is called vaporization. The same phenomenon is called evaporation when heating is categorised to be done below the boiling point of the liquid.
5. Boiling Point The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon and varies from place to place. The boiling point of water at normal pressure is 100ºC.
6. Condensation It is the process in which gas changes into the liquid state or liquid changes to solid state i.e., solidification.
7. Latent Heat The word latent means hidden. Thus, latent heat is the amount of heat absorbed or released by a substance undergoing a change of state such as ice changing to water or water to steam at a constant temperature.

Latent heat of fusion is defined as the amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point. Particles in water at 0ºC have more energy as compared to particles in ice at the same temperature, because of the presence of latent heat of fusion. Latent heat of vaporization is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point. Temperature remains constant during boiling due to the latent heat of vaporization.

Effect of Change of Temperature

On heating the solid, kinetic energy of the particles increases. Due to which they start vibrating with greater speed (at their fixed position). The energy supplied by the heat overcomes the forces of attraction between the  particles. Due to reduction in force of attraction, the particles leave their fixed position and start moving freely. Due to this, a stage reached when solid melts and starts to convert into liquid.

Effect of Change of Pressure

By increasing pressure and reducing temperature, we can change a gas into liquid and a liquid into solid and reverse is achieved by decreasing pressure and increasing temperature.

• Due to the latent heat of vaporization, particles in steam, ie. water vapor at 373 K (100ºC) have more energy than that of water at the same temperature. That’s why steam causes severe burns than that of water at 100ºC.
• At high altitudes, atmospheric pressure is low, therefore, the vapor pressure of a liquid becomes equal to atmospheric pressure at low temperature, i.e., water boils at a temperature less than 100ºC and hence, food requires more time to cook.
• Inside the pressure cooker, the pressure is high and hence, water boils at a temperature higher than 100ºC. Thus, less time required to cook the food.
• In the presence of the impurity, boiling point increases, and freezing point decreases.
• Solid carbon dioxide is stored under high pressure. It gets converted directly to gaseous state on decreasing pressure to 1 atm without coming into the liquid state. That’s why it is also called ‘dry ice’ or ‘dry cold‘.

As we look at our surroundings, we see a large variety of things with different shapes, sizes and textures. Everything in this universe is made up of material which scientists have named ‘matter’. All the things such as stones, clouds, food, stars, plants, even a small drop of water occupy space and have mass. In other words, the matter is something which has mass, occupy volume, can have physical resistance, inertia and can be realized by the sense organs. Philosophers classified matter in the matter in form of five basic elements- air, earth, fire, sky, and water. According to them, everything, living or non-living was made up of these five basic elements.

Properties of Matter

1. Matter is made up of very small particles that are beyond our imagination
2. The particles have space in between them, called the intermolecular space
3. They are continuously moving i.e, they possess kinetic energy. As the temperature rises, Speed of the particles increases. Due to which the kinetic energy of the particles increases.
4. They attract each other. The force of attraction responsible for keeping them together is called intermolecular force.
5. The strength of this force of attraction varies from one kind of matter to another.

Particles of Matter

Matter has mainly two particles Atoms The word atom has been derived from Greek word atomos meaning indivisible. AN atom is the smallest particles of an element that may or may not exist independently and retain all its chemical properties i.e., takes part in chemical reactions. Atoms of different elements have different masses and chemical properties. Molecules A molecule is a group of two or more atoms that are chemically bonded together. It can be defined as the smallest particle of an element or a compound that is capable of independent existence and shows all the properties of that substance. However, it does not take part in a chemical reaction. Types of Molecules These are of two types

1. Homomolecules or Molecules of the Element: These are the molecules of an element constituted by the same type of atoms. e.g., O2, H2, H2, N2 etc. The number of atoms constituting a molecule is called its atomicity. e.g., atomicity of phosphorus (P4) is four and of sulfur (S8) is eight.
2. Heteromolecular or molecules of the compounds In these molecules, atoms of different elements join together in definite proportions.

Examples of Heteromolecules

Compound	Combining Elements	Ratio by Mass
Water (H2O)	Hydrogen, Oxygen	1:8
Ammonia (NH3)	Nitrogen, hydrogen	14:3
Carbon dioxide (CO2)	Carbon, oxygen	3:8

 

The theory of Dalton did not hold long and it was proved through the experiments of research worker like JJ Thomson (1897), Rutherford (1911), Neils Bohr (1912), Vector Chidwick, Moseley etc., that atom is made up of smaller particles, called the subatomic particles like electron, proton, neutron, positron, neutrino meson etc. However, former three are considered as the fundamental particles and later are appeared only for a short instance during the microparticles exchange mechanism. Thus, these are not fundamental particles.

The Subatomic particles named for the weak force is the wboson

Fundamental Particles

Electrons, protons, and neutrons are the fundamental particles of atom, discovery and properties of which are as follows. a) Discovery of Electrons (-1eº) Electron was discovered in cathode rays experiments by JJ Thomson in 1877. In this experiment, when the pressure of a discharge tube maintained at high potential is reduced to 10^-6 atm, a stream of negatively charged particles, called electrons, is originated from cathode. These rays were called cathode rays. Characteristics of these rays and their particles are

1. These rays themselves are not visible but their behaviour can be observed with the help of fluorescent or phosphorescent materials. (Note that television picture tubes are cathode ray tubes).
2. In the presence of electrical or magnetic field, the behaviour of cathode rays are similar to that expected from negatively charged particles, called electrons.
3. The carge on an elecctron, i.e., –1.602 x 10^-19C was determined by Mulikan through oil drop experiment.
4. Actual mass of an electron i.e., 9.11x 10^-31kg was calculated by JJ Thomson. Of the three fundamental particles of an atom, electron is the lightest.
5. e/m ratio (specific charge) of electrons was determined by Thomson as 1.76x 10⁸ C/g.
6. e/m ratio of the electron was found to be independent of the nature of gas and electrode used. Therefore, electrons are fundamental particles of all kinds of matter.

b) Discovery of Protons Even before the electron was identified, E Goldstein in 1886 discovered the presence of new radiation in a gas discharge and called them canal rays. These rays were positively charged radiations which ultimately led to the discovery of another sub-atomic particle. This sub-atomic particle had a charge, equal in magnitude but opposite in sign to that of the electron. It was given the name proton by Rutherford in 1919. Mass of proton is 1.67 x 10^-27 kg while its charge is +1.6x 10^-19 C. c) Discovery of Neutrons The positive charge of a nucleus is due to the positvely charged particles called protons alone. There is another sub atomic particle called neutron, identified by Chadwick (1932) by bombarding a thin sheet of beryllium by α-particles. Neutrons are electrically neutral particles (i.e., have no charge) having a mass slightly greater than that of the protons. Mass of neutron is 1.67×10^-27 kg (i.e., nearly equal to that of proton).

Non-Fundamental Particles

Particles other than electrons, protons and neutrons are called non-fundamental particles. a) Positron: It was discovered by Anderson in 1932. It is the antiparticle of electron (i.d., its charge is positive and its mass is equal to that of the mass of electron). Its symbol is e^-+. b) Antiproton. It is the antiparticle of proton. It was discovered in 1955. Its charge is –e and its mass is equal to that of the mass of proton. Its symbol is p. For every fundamental particle, there exists an identical fundamental particle just opposite in some property. It is called antiparticle of that fundamental particle. e.g., Electron and positron are identical in all respects, except that charge on them are opposite. So, positron is an antiparticle of electron. c) Neutrino and Antineutrino The existence of these particles was predicted in 1930 by Pauli while explaining the emission of β-particles from radioactive nuclei, but these particles were actually observed experimentally in 1956. Their rest mass and charge both are zero, but they have energy and momentum. These are mutually antiparticles of each other. d) Pi-mesons The existence of π-mesons was predicted by Yukawa in 1935, but they were actually discovered in 1947 in cosmic rays. Nuclear forces are explained by exchange of π mesons between the nucleons, Π-mesons are of three types- positive pi-meson, negative pi-mesons, and neutral pi-mesons. The mass of pi-mesons positive is 274 times the mass of the electron and Pi-neutral mesons nearly 264 times the electronic mass. e) Quarks and Bosons: The elementary particles from which other heavy sub-atomic particles like protons, neutron, etc are formed, are called quarks. These particles carry fractional charge. Bosons are the particles for which number of rotations are whole number.

Boson→Meson+Photon