Classification of Matter
~8 min read
- Element/Compound/Mixture: Element = one type of atom. Compound = atoms of different elements bonded. Mixture = physical combination.
- States of matter: Solid (fixed shape, volume), Liquid (fixed volume, no shape), Gas (no fixed shape or volume), Plasma (ionised gas — sun, lightning).
- Homogeneous vs heterogeneous: Homogeneous mixture has uniform composition (salt water). Heterogeneous doesn't (sand in water).
All matter belongs to one of these categories. NDA tests pure substances vs mixtures, states of matter, and concepts like colloids, suspensions, solutions.
Types of Matter
| Type | Definition | Examples |
|---|---|---|
| Element | Cannot be broken down chemically. One type of atom | H, O, Fe, Au, Na |
| Compound | Two or more elements chemically bonded. Definite ratio | H₂O, CO₂, NaCl, CH₄ |
| Mixture (Homogeneous) | Uniform composition throughout. Single phase | Salt solution, alloys, air |
| Mixture (Heterogeneous) | Non-uniform; visibly different parts | Sand in water, oil and water, soil |
States of Matter
| State | Shape | Volume | Particle arrangement |
|---|---|---|---|
| Solid | Fixed | Fixed | Tightly packed, vibrating in place |
| Liquid | No fixed | Fixed | Close, can slide past each other |
| Gas | No fixed | No fixed | Far apart, random motion |
| Plasma | No fixed | No fixed | Ionised gas; positive ions + free electrons. Sun, lightning, neon lights |
Bose-Einstein Condensate (BEC): Fifth state of matter, at temperatures near absolute zero. Predicted by Bose and Einstein (1924); first observed 1995.
Changes of State
| From | To | Name |
|---|---|---|
| Solid | Liquid | Melting / Fusion |
| Liquid | Gas | Vaporisation (slow: Evaporation; fast: Boiling) |
| Solid | Gas | Sublimation (camphor, naphthalene, dry ice) |
| Gas | Liquid | Condensation |
| Liquid | Solid | Freezing |
| Gas | Solid | Deposition (frost formation) |
Solutions, Suspensions, Colloids
- True solution: Particles < 1 nm. Transparent, stable, no settling. Salt in water.
- Colloid: Particles 1-1000 nm. Shows Tyndall effect (light beam scattering). Milk, fog, ink, blood.
- Suspension: Particles > 1000 nm. Particles settle on standing. Sand in water, muddy water.
- Tyndall effect: Scattering of light by colloidal particles. Why a beam of light is visible in dusty air or fog.
NDA PYQ Examples
Q: Which is a compound?
(a) Iron (b) Air (c) Water (d) Brass
Answer: (c) Water — H₂O, chemical combination of H and O.
Q: The fourth state of matter is:
(a) Liquid crystal (b) Plasma (c) Glass (d) BEC
Answer: (b) Plasma — ionised gas, found in stars, lightning, neon lights.
Q: Sublimation is conversion from:
(a) Solid to liquid (b) Liquid to gas (c) Solid to gas directly (d) Gas to liquid
Answer: (c) Solid to gas directly — without passing through liquid state. Camphor, dry ice.
Q: Milk is an example of:
(a) True solution (b) Suspension (c) Colloid (d) Mixture only
Answer: (c) Colloid — fat globules dispersed in water.
Drill Classification of Matter for NDA
NDA-pattern items on Classification of Matter with answer keys and explanations.
Start Free Mock TestFrequently Asked Questions
What is the difference between a compound and a mixture?
Compound: chemically bonded elements in fixed ratios (H₂O always has 2H : 1O). Cannot be separated by physical means. Mixture: physical combination, variable composition (salt water can have any salt:water ratio). Can be separated physically.
Why does dry ice produce smoke?
Dry ice is solid CO₂ that sublimes directly to CO₂ gas at -78.5°C. The cold gas chills surrounding air, condensing water vapour into tiny droplets — the visible 'smoke' is water mist, not the CO₂.
Why is air a mixture and not a compound?
Air's composition varies (78% N₂, 21% O₂, 1% Ar, ~0.04% CO₂, water vapour). The constituents are not chemically bonded; they can be separated by fractional distillation of liquid air.
What is the Tyndall effect?
Scattering of light by particles in a colloid. Why a torch beam is visible passing through fog, dust-filled air, or a glass of milk diluted with water. Not seen in true solutions (particles too small).
What is plasma?
Ionised gas — atoms have been stripped of electrons. Conducts electricity. Found in stars (including the sun), lightning bolts, neon signs, fluorescent lamps, plasma TVs. ~99% of visible matter in the universe is plasma.