Everything around us – the air we breathe, the water we drink, the food we eat and even our own body – is made of matter. Understanding what matter is made of, the different states in which it exists and how it can be classified is the foundation of chemistry. This chapter is a regular source of questions in the General Science part of competitive exams.
What is Matter?
Anything that has mass and occupies space (volume) is called matter. Air, water, stone, wood and plants are all matter. Light, heat, sound and feelings like love or fear are not matter, because they have no mass and do not occupy space.
Ancient Indian philosophers grouped matter into five basic elements called Panch Tatva – earth (prithvi), water (jal), fire (agni), air (vayu) and sky (akash). Modern science classifies matter on the basis of its physical and chemical nature.
Characteristics of Particles of Matter
- Matter is made up of extremely small particles.
- There are spaces between these particles – this is why sugar dissolves in water without raising its level much.
- The particles are continuously moving; their kinetic energy increases with temperature.
- The particles attract each other. This force of attraction is strongest in solids and weakest in gases.
Diffusion: The spontaneous mixing of particles of two substances is called diffusion. It is fastest in gases, slower in liquids and slowest in solids. The smell of incense or perfume spreading across a room is an example.
Components of Matter: Atoms and Molecules
The Indian sage Maharishi Kanad proposed that matter can be divided until we reach the smallest particle, which he called "Parmanu". In 1808, the English scientist John Dalton gave the modern atomic theory.
- Atom: the smallest particle of an element that takes part in a chemical reaction.
- Molecule: the smallest particle of an element or compound that can exist independently and shows all its properties. Example: O2, H2O.
Sub-atomic Particles
| Particle | Charge | Mass | Location | Discovered by |
|---|---|---|---|---|
| Electron | Negative (−1) | 9.1 × 10-31 kg (about 1/1836 of a proton) | Orbits around the nucleus | J.J. Thomson (1897) |
| Proton | Positive (+1) | 1.67 × 10-27 kg | Nucleus | E. Goldstein observed canal rays (1886); Rutherford identified and named the proton |
| Neutron | No charge | Slightly more than a proton | Nucleus | James Chadwick (1932) |
- The nucleus was discovered by Ernest Rutherford (1911) through the gold foil (alpha-particle scattering) experiment.
- Niels Bohr (1913) proposed that electrons move in fixed orbits (shells) of definite energy.
- Atomic number (Z) = number of protons. Mass number (A) = protons + neutrons.
- The ordinary hydrogen atom (protium) has no neutron.
- Isotopes have the same atomic number but different mass numbers (e.g., protium, deuterium and tritium of hydrogen). Isobars have the same mass number but different atomic numbers (e.g., 40Ar and 40Ca).
States of Matter
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes the shape of the container | No fixed shape |
| Volume | Fixed | Fixed | No fixed volume – fills the container |
| Space between particles | Very little | More than solids | Very large |
| Force of attraction | Strongest | Moderate | Weakest |
| Compressibility | Negligible | Very little | Highly compressible |
| Ability to flow | Does not flow | Flows | Flows easily |
| Kinetic energy of particles | Lowest | Moderate | Highest |
Because gases are highly compressible, LPG (Liquefied Petroleum Gas) can be filled in cylinders and CNG (Compressed Natural Gas) is used as fuel in vehicles.
Fourth and Fifth States of Matter
- Plasma (fourth state): a super-heated gas of ions and free electrons. It is found in the Sun and stars, lightning, and in neon signs and fluorescent tubes.
- Bose–Einstein Condensate (BEC) (fifth state): formed when a gas of very low density is cooled to near absolute zero. It was predicted in 1924–25 by the Indian physicist Satyendra Nath Bose and Albert Einstein, and first produced in the laboratory in 1995 by Eric Cornell and Carl Wieman (with Wolfgang Ketterle also achieving it that year), who received the Nobel Prize in Physics in 2001.
Remember: The particles called bosons are named after S.N. Bose. Absolute zero is 0 K = −273.15°C.
Change of State
| Process | Change | Example |
|---|---|---|
| Melting (fusion) | Solid → Liquid | Ice melting into water at 0°C |
| Freezing (solidification) | Liquid → Solid | Water turning into ice |
| Vaporisation (boiling / evaporation) | Liquid → Gas | Water boiling at 100°C |
| Condensation | Gas → Liquid | Water drops on the outside of a cold glass |
| Sublimation | Solid → Gas directly | Camphor, naphthalene balls, ammonium chloride, iodine, dry ice |
| Deposition | Gas → Solid directly | Formation of frost |
- Melting point of ice: 0°C (273.15 K). Boiling point of water: 100°C (373.15 K) at normal atmospheric pressure.
- Increasing pressure raises the boiling point – this is how a pressure cooker cooks food faster.
- At high altitudes, air pressure is low, so water boils below 100°C and food takes longer to cook.
- Dry ice is solid carbon dioxide; it changes directly into gas when pressure is reduced.
Latent Heat
The heat energy absorbed or released during a change of state, without any change in temperature, is called latent (hidden) heat.
- Latent heat of fusion of ice ≈ 334 J/g (80 cal/g).
- Latent heat of vaporisation of water ≈ 2260 J/g (540 cal/g).
- This is why burns from steam are more severe than burns from boiling water at the same temperature – steam releases its extra latent heat on the skin.
- Ice at 0°C cools a drink better than water at 0°C, because ice absorbs latent heat while melting.
Evaporation
Evaporation is the change of a liquid into vapour at any temperature below its boiling point. It is a surface phenomenon and always causes cooling.
- The rate of evaporation increases with more surface area, higher temperature, higher wind speed and lower humidity.
- Water in an earthen pot (matka) stays cool because water seeps out through pores and evaporates.
- We sweat more in summer; the evaporation of sweat cools our body. Cotton clothes absorb sweat and help it evaporate.
- Clothes dry slowly on a humid, rainy day.
Classification of Matter
On the basis of chemical composition, matter is divided into pure substances and mixtures.
- Pure substances have a fixed composition and the same properties throughout. They are of two types – elements and compounds.
- Mixtures contain two or more substances mixed in any proportion, without any chemical combination.
Types of Mixtures
| Homogeneous mixture | Heterogeneous mixture |
|---|---|
| Uniform composition throughout; components cannot be seen separately | Non-uniform composition; components can often be seen |
| Examples: salt in water, sugar solution, air, alloys like brass and bronze, vinegar | Examples: sand and water, oil and water, soil, salt and iron filings |
Solution, Suspension and Colloid
| Property | True solution | Colloid | Suspension |
|---|---|---|---|
| Nature | Homogeneous | Appears homogeneous but is heterogeneous | Heterogeneous |
| Particle size | Less than 1 nm | 1 nm to 100 nm | More than 100 nm |
| Particles settle? | No | No | Yes |
| Tyndall effect (scattering of light) | No | Yes | Yes |
| Examples | Sugar or salt in water | Milk, fog, smoke, butter, cheese, jelly, shaving cream | Muddy water, chalk powder in water, sand in water |
Tyndall effect: the scattering of a beam of light by colloidal particles, which makes the path of light visible – for example, sunlight passing through a dense forest canopy or a beam of light in a dusty room. It is named after John Tyndall.
Methods of Separating Mixtures
| Method | Used to separate |
|---|---|
| Evaporation | A dissolved solid from its solution (salt from sea water) |
| Filtration | Insoluble solid from a liquid (sand from water) |
| Sedimentation and decantation | Heavy insoluble particles that settle down (rice washing, muddy water) |
| Centrifugation | Cream from milk; blood cells from plasma; in washing machine dryers |
| Sublimation | A sublimable solid from a non-sublimable one (camphor or ammonium chloride from salt) |
| Chromatography | Different coloured components (dyes) in ink; drugs in blood |
| Distillation | Two miscible liquids with a large difference in boiling points (acetone and water); pure water from salt water |
| Fractional distillation | Liquids with close boiling points; components of petroleum and of liquefied air |
| Separating funnel | Two immiscible liquids (oil and water; kerosene and water) |
| Magnetic separation | Iron filings from sand or sulphur |
| Crystallisation | Pure solid crystals from an impure solution (purifying salt, alum, copper sulphate) |
| Winnowing, sieving, threshing, handpicking | Common household and farm methods for grains |
Physical and Chemical Changes
| Physical change | Chemical change |
|---|---|
| No new substance is formed | One or more new substances are formed |
| Usually reversible | Usually irreversible |
| Examples: melting of ice, dissolving sugar, tearing paper, boiling water, magnetising iron | Examples: burning of paper, rusting of iron, cooking food, curdling of milk, digestion of food, ripening of fruits |
Quick Revision Points
- Diffusion is fastest in gases.
- Electron – J.J. Thomson (1897); Neutron – James Chadwick (1932); Nucleus – Rutherford (1911).
- Plasma is the fourth state; Bose–Einstein Condensate is the fifth state.
- Camphor, naphthalene, iodine and dry ice show sublimation.
- Steam burns are worse due to latent heat of vaporisation.
- Evaporation causes cooling; it is a surface phenomenon.
- Milk is a colloid; air and brass are homogeneous mixtures.
- Cream is separated from milk by centrifugation; petroleum is refined by fractional distillation.
Read also: Elements and Compounds
Practice MCQs
1. Which of the following is NOT matter?
(a) Air
(b) Water vapour
(c) Light
(d) Dust
2. The neutron was discovered by:
(a) J.J. Thomson
(b) Rutherford
(c) James Chadwick
(d) Niels Bohr
3. Which Indian scientist is linked with the fifth state of matter?
(a) C.V. Raman
(b) S.N. Bose
(c) Homi Bhabha
(d) Meghnad Saha
4. Naphthalene balls disappear with time due to:
(a) Evaporation
(b) Melting
(c) Sublimation
(d) Condensation
5. Food cooks faster in a pressure cooker because:
(a) Boiling point of water decreases
(b) Boiling point of water increases
(c) Heat is lost slowly
(d) Steam is not formed
6. Which of the following is a colloid?
(a) Salt solution
(b) Milk
(c) Muddy water
(d) Sugar solution
7. Cream is separated from milk by:
(a) Filtration
(b) Distillation
(c) Centrifugation
(d) Sublimation
8. Different components of petroleum are separated by:
(a) Simple distillation
(b) Fractional distillation
(c) Chromatography
(d) Crystallisation
9. The state of matter found in the Sun and stars is:
(a) Solid
(b) Liquid
(c) Plasma
(d) Bose–Einstein Condensate
10. Which of the following is a chemical change?
(a) Melting of wax
(b) Dissolving salt in water
(c) Rusting of iron
(d) Freezing of water
Answers: 1 – (c) | 2 – (c) | 3 – (b) | 4 – (c) | 5 – (b) | 6 – (b) | 7 – (c) | 8 – (b) | 9 – (c) | 10 – (c)
Reference: NCERT Science Class IX (Matter in Our Surroundings; Is Matter Around Us Pure; Atoms and Molecules; Structure of the Atom).