Matter in Our Surroundings • Topic 1 of 3

States of Matter & their Properties

Look around you. The chair you sit on, the water you drink, the air you breathe — all of these are matter. Matter is anything that has mass and occupies space (has volume). Early Indian philosophers spoke of five tattva (panch tatva), but modern science gives us a sharper picture, built around the idea that matter is made of tiny particles.

The particle nature of matter

A few simple observations tell us what these particles are like:

  • Particles are extremely small. Dissolve a few crystals of potassium permanganate (KMnO4) in water and keep diluting — the colour persists through millions of particles, showing each crystal contains a huge number of tiny particles.
  • Particles have spaces between them. When sugar dissolves in a full glass of water, the level does not overflow — the sugar particles slip into the gaps between water particles.
  • Particles are continuously moving. They possess kinetic energy, which increases with temperature. This non-stop motion is why we can smell hot food from across the room.
  • Particles attract one another. The strength of this force of attraction differs from one kind of matter to another, and it decides whether a substance is a solid, a liquid or a gas.

Diffusion

The intermixing of particles of two different substances on their own is called diffusion. Diffusion is fastest in gases (particles move freely and fast), slower in liquids, and almost negligible in solids. Raising the temperature speeds up diffusion because the particles move faster.

The three states of matter

Matter exists mainly in three physical states — solid, liquid and gas — which differ in how tightly the particles are packed and how strongly they attract each other.

  • Solids have a fixed shape and fixed volume. The particles are packed very close, the force of attraction is very strong, and they only vibrate about fixed positions. Solids are nearly incompressible, are rigid and have high density.
  • Liquids have a fixed volume but no fixed shape — they take the shape of the container. The particles are a little further apart and can slide past one another, so liquids flow (they are fluids) and diffuse moderately.
  • Gases have neither fixed shape nor fixed volume. The particles are far apart with very weak attraction and move rapidly in all directions. Gases are highly compressible (this is how we fill CNG and LPG cylinders), have very low density and diffuse the fastest.

Beyond the three states

Plasma is a fourth state made of super-energetic, ionised (charged) particles; it glows, as in the Sun, the stars and a fluorescent tube. Bose–Einstein Condensate (BEC) is a fifth state formed when a gas is cooled to nearly absolute zero (about −273°C), where particles lose almost all energy and behave as a single entity.

Particle arrangement: tightly packed in a solid, loosely packed in a liquid, far apart in a gasSOLIDLIQUIDGASParticles spread out as we go solid to gas
Solved Examples
1
Worked Example
Why does a gas fill the whole container it is put into, but a solid does not?
Solution
  1. In a gas the particles are very far apart with extremely weak forces of attraction.
  2. They move rapidly and randomly in all directions, so they spread out until they hit the walls.
  3. In a solid the particles are tightly held in fixed positions by strong attractive forces; they can only vibrate.

Answer: A gas spreads to fill the container because its particles are free and fast-moving; a solid keeps its shape because its particles are locked in place.

2
Worked Example
When 50 g of sugar is dissolved in a full glass of water, the water does not overflow. Explain.
Solution
  1. There are empty spaces between the particles of water.
  2. The sugar particles separate and slip into these inter-particle spaces.
  3. So the total volume does not increase enough to overflow.

Answer: The sugar particles occupy the gaps between water particles, so the level stays the same — proof that matter has spaces between its particles.

3
Worked Example
Arrange solid, liquid and gas in increasing order of (a) compressibility and (b) density.
Solution
  1. Compressibility depends on the empty space between particles — most in gas, least in solid.
  2. So compressibility: solid < liquid < gas.
  3. Density depends on how closely packed the particles are — most packed in solid.
  4. So density: gas < liquid < solid.

Answer: (a) Compressibility: solid < liquid < gas. (b) Density: gas < liquid < solid.

4
Worked Example
We can smell incense (agarbatti) from a distance. Which property of matter does this show, and how is it affected by temperature?
Solution
  1. The smell reaches us because the fragrance particles spread out and mix with air particles — this is diffusion.
  2. Diffusion happens because particles are in continuous motion.
  3. On a hot day the particles have more kinetic energy and move faster, so the smell spreads quicker.

Answer: It shows diffusion (continuous motion of particles); diffusion becomes faster as temperature rises.

5
Worked Example
A diver finds that a drop of ink released in a tank of still water slowly colours the whole tank without stirring. Name and explain this process.
Solution
  1. The ink particles mix into the water on their own — this is diffusion.
  2. Both ink and water particles are moving continuously and have spaces between them.
  3. Over time the moving ink particles spread evenly through the gaps in the water.

Answer: The process is diffusion of ink in water, caused by the continuous random motion of particles and the spaces between them.

6
Worked Example
State whether each is true or false, with a reason: (a) A liquid has a fixed shape. (b) Plasma is made of ordinary uncharged particles.
Solution
  1. (a) A liquid takes the shape of its container; only its volume is fixed.
  2. So statement (a) is false.
  3. (b) Plasma consists of super-energetic, ionised (charged) particles, not ordinary uncharged ones.
  4. So statement (b) is also false.

Answer: (a) False — a liquid has fixed volume but no fixed shape. (b) False — plasma is made of ionised (charged) particles.

Key Points

  • Matter is anything that has mass and occupies space; it is made of tiny, moving particles with spaces between them and forces of attraction.
  • Key particle properties: very small, have inter-particle spaces, are in continuous motion, and attract each other — shown by experiments like KMnO4 dilution and dissolving sugar.
  • Diffusion (self-mixing of particles) is fastest in gases, slower in liquids, negligible in solids, and increases with temperature.
  • Solids are rigid, incompressible, dense (fixed shape and volume); liquids flow and have fixed volume but no fixed shape; gases are highly compressible with neither fixed shape nor volume.
  • Plasma (ionised particles, as in the Sun) and Bose–Einstein Condensate (gas cooled near −273°C) are the fourth and fifth states of matter.
Quick Check — 5 MCQs
Tap an option to check your answer0 / 5
Q1.Which state of matter has a fixed volume but no fixed shape?
Explanation: A liquid keeps its volume but flows to take the shape of its container.
Q2.The continuous self-mixing of particles of two substances is called:
Explanation: Diffusion is the intermixing of particles on their own, due to their continuous motion.
Q3.Gases are highly compressible mainly because:
Explanation: Large inter-particle spaces let gas particles be pushed closer, so gases compress easily.
Q4.Which is the correct order of density?
Explanation: Particles are most closely packed in solids and least in gases, so gas < liquid < solid.
Q5.The fourth state of matter, found in the Sun and stars, is:
Explanation: Plasma is a glowing state of ionised, super-energetic particles, as in the Sun.
Practice more MCQs → 📝 Assignment · 30 marks