Everything around us — air, water, food, your phone — is made of matter. This module explains what matter is, how it behaves, and the concepts that show up in CDS, NDA & AFCAT every year.
In this module you'll learn: what matter is, its states and changes, the difference between elements, compounds and mixtures, and important separation techniques. All of these appear directly in CDS/NDA/AFCAT questions.
Matter is anything that has mass and occupies space (volume). If you can touch it, smell it, or weigh it — it's matter.
Water ✓ · Air ✓ · Iron ✓ · Smoke ✓
Light ✗ · Sound ✗ · Heat ✗ · Electricity ✗
(These are forms of energy — NOT matter)
Imagine trying to put something in a bag. If it fills the bag and weighs something — it's matter. You can't bag light or sound — so they're not matter.
Heat, light, sound, electricity and shadow are NOT matter. This is a very common trick question in CDS/AFCAT.
Matter exists in three main states: solid, liquid and gas. The difference is in how tightly the particles (atoms/molecules) are packed and how freely they move.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | No fixed shape | No fixed shape |
| Volume | Fixed | Fixed | No fixed volume |
| Particle arrangement | Very tightly packed | Loosely packed | Very far apart |
| Particle movement | Only vibrate | Slide past each other | Move freely |
| Compressibility | Not compressible | Barely compressible | Highly compressible |
| Example | Ice, iron, wood | Water, oil, mercury | Steam, oxygen, CO₂ |
Mercury is a metal but it is a liquid at room temperature. Bromine is the only non-metal liquid at room temperature. Both are frequent trick answers.
Matter changes from one state to another when heat is added or removed. Each change has a specific name:
| Change | Process Name | Heat |
|---|---|---|
| Solid → Liquid | Melting (Fusion) | Added |
| Liquid → Solid | Freezing (Solidification) | Removed |
| Liquid → Gas | Vaporisation / Evaporation | Added |
| Gas → Liquid | Condensation | Removed |
| Solid → Gas | Sublimation | Added |
| Gas → Solid | Deposition | Removed |
Ice melting → melting. Water boiling → vaporisation. Dew forming on grass → condensation. Snow forming from water vapour in clouds → deposition.
This is one of the most tested topics in General Science. The key question is: does the substance become something new?
| Feature | Physical Change | Chemical Change |
|---|---|---|
| New substance formed? | No | Yes |
| Reversible? | Usually yes | Usually no |
| Chemical composition | Unchanged | Changed |
| Energy change | Small | Large |
| Examples | Melting ice, tearing paper, dissolving sugar | Burning wood, rusting iron, cooking egg |
All matter is either a pure substance or a mixture. Pure substances have a fixed composition throughout.
Think of elements as single Lego colours. Compounds are specific Lego structures built from those colours in fixed ratios. Mixtures are random piles of Lego — any colour, any amount.
| Type | Definition | Examples |
|---|---|---|
| Element | Made of ONE type of atom only. Cannot be broken down further by chemical means. | Gold (Au), Oxygen (O), Iron (Fe), Carbon (C) |
| Compound | Two or more elements combined chemically in a fixed ratio. Has new properties different from its elements. | Water (H₂O), Salt (NaCl), CO₂, Rust (Fe₂O₃) |
A mixture contains two or more substances mixed together but not chemically combined. Each substance keeps its own properties.
| Feature | Homogeneous Mixture | Heterogeneous Mixture |
|---|---|---|
| Appearance | Same throughout (uniform) | Different in different parts |
| Can you see the parts? | No | Yes (sometimes) |
| Also called | Solution | Suspension / Colloid |
| Examples | Salt water, air, alloys, vinegar | Sand + water, salad, granite, smoke |
Alloys (brass, bronze, steel) are mixtures — NOT compounds, even though they look like metals. This is very commonly asked. Brass = copper + zinc. Bronze = copper + tin. Steel = iron + carbon.
Since mixture components keep their individual properties, we can use those properties to separate them. Each method is based on a specific physical property.
| Method | Based On | Used For | Example |
|---|---|---|---|
| Filtration | Particle size | Insoluble solid from liquid | Sand from water |
| Evaporation | Volatility | Dissolved solid from solution | Salt from seawater |
| Distillation | Boiling point | Liquids with different boiling points | Water from alcohol |
| Fractional Distillation | Boiling point differences | Liquids with close boiling points | Crude oil refining, air separation |
| Chromatography | Adsorption / solubility | Dyes, pigments, inks | Separating ink colours |
| Centrifugation | Density / particle size | Cream from milk, blood components | Dairy, medical labs |
| Magnetic separation | Magnetic property | Magnetic from non-magnetic | Iron from sulphur |
| Sublimation | Subliming property | Sublimable solid from non-sublimable | Camphor from salt |
| Crystallisation | Solubility | Pure solid from impure solution | Sugar crystals, alum |
These are three types of mixtures, classified by the size of particles dispersed in them.
| Feature | Solution | Colloid | Suspension |
|---|---|---|---|
| Particle size | <1 nm | 1–100 nm | >100 nm |
| Appearance | Clear/transparent | Cloudy, translucent | Opaque, settles |
| Passes through filter? | Yes | Yes | No |
| Settles on standing? | No | No | Yes |
| Tyndall Effect? | No | Yes | Yes |
| Examples | Salt water, air, brass | Milk, fog, blood, jelly | Chalk in water, muddy water |
Milk is a colloid (emulsion — fat droplets in water), NOT a solution. Blood is also a colloid. Fog and clouds are colloids (aerosol). This distinction is frequently tested.
Every substance has properties that help us identify and use it. They fall into two groups:
| Physical Property | Chemical Property |
|---|---|
| Observed/measured without changing the substance | Observed only when substance undergoes a reaction |
| Colour, smell, density, melting point, boiling point, hardness, solubility, conductivity | Flammability, reactivity with acid, rusting, ability to oxidise/reduce |
| No new substance formed | New substance formed |
Use this page for last-minute revision before your exam. All the high-yield facts from this module, organised for quick scanning.