Curriculum
Science Grade 9
Chapter 1: MATTER IN OUR SURROUNDINGS
Grade 9 Science | Chapter 1
Matter in Our Surroundings
Everything in the universe — from a grain of sand to a distant star — is made of matter. In this chapter we explore what matter is, how its tiny particles behave, the three states it can exist in, and how it changes from one state to another.
|
3 States of Matter |
3 Key Properties |
10+ Worked Examples |
4 Practice Sets |
☰ Contents
|
1. Introduction to Matter 2. Physical Nature of Matter 3. Characteristics of Particles 4. States of Matter 5. State Diagrams Explained |
6. Change of State 7. Evaporation 8. Worked Examples (10) 9. Practice Sets A – D 10. Summary & Exam Quick-Check |
|
1. Introduction to Matter |
Look around you right now. The chair you sit on, the air filling your lungs, the water in your bottle, the clouds outside — all of it is matter. Scientists define matter as anything that occupies space and has mass. Two measurable quantities confirm something is matter: its mass (measured in kilograms, kg) and its volume (measured in cubic metres, m³, though litres are common in everyday use).
Ancient Indian philosophers grouped all matter into five basic elements they called the Panch Tatva: air, earth, fire, sky, and water. Ancient Greek thinkers arrived at a remarkably similar classification. Modern science has moved beyond these ideas, but the same curiosity drives us — understanding what things are made of and why they behave as they do.
Today, scientists classify matter in two broad ways: by its physical properties (which this chapter covers) and by its chemical nature (covered in later chapters). In this chapter our focus is on the physical world of matter.
📚 Core Definition
Matter is anything that has mass and occupies space (volume). It is composed of extremely tiny particles that are in constant motion and attract one another.
|
2. Physical Nature of Matter |
For a long time, two competing ideas existed: one group believed matter was continuous — like a solid block of wood that has no gaps. Another group believed matter was particulate — made of tiny pieces, like sand on a beach. Simple observation helps settle the question.
When you dissolve a spoonful of sugar in a glass of water, the water level barely changes, yet the sugar has clearly gone somewhere — it has spread through the spaces between water particles. This tells us matter must be made of particles with spaces between them.
▶ Diagram 1 — Salt Dissolving in Water (Particle Model)
|
Before Adding Salt Water particles only |
Adding Salt ● Salt entering spaces |
After Dissolving Salt evenly distributed |
Fig. 1 — Salt particles (orange) fill the gaps between water particles (blue). Water level stays unchanged because salt occupies existing spaces, not new ones.
|
3. Characteristics of Particles of Matter |
Every particle of matter — no matter how large or small the object — shares three fundamental characteristics:
❶ Particles Have Spaces Between Them
When sugar or salt dissolves in water, those particles do not create extra space — they slot into the gaps that already existed between water particles. When we make tea or lemonade, the same thing happens. This space between particles is called interparticle space, and it is greatest in gases and smallest in solids.
❷ Particles Are Continuously Moving
Particles of matter are never still — they are always in motion. The energy possessed by a particle due to its motion is called kinetic energy. As temperature rises, particles move faster, meaning their kinetic energy increases. This continuous motion explains a very important process called diffusion — the mixing of particles of two different substances on their own, without being stirred.
Examples: the smell of an incense stick spreading across a room; ink spreading through water; the aroma of cooking reaching you from the kitchen.
❸ Particles Attract Each Other
There is a force of attraction pulling particles of matter toward one another. This is called interparticle force of attraction. The strength varies between substances — it is greatest in solids (particles are held tightly together), intermediate in liquids, and weakest in gases. This is why solids hold their shape, liquids flow, and gases fill any container they are placed in.
▶ Comparing Diffusion Rates
| Type of Diffusion | Speed | Reason | Example |
| Gas into Gas | Fastest | Particles move freely at high speed; large interparticle spaces | Perfume smell spreading in a room |
| Liquid into Liquid | Moderate | Particles move but are closer together than in gases | Ink spreading in water |
| Solid into Liquid | Slowest | Solid particles are tightly packed; very small interparticle spaces | Copper sulphate crystal colouring water over days |
|
4. States of Matter |
Matter exists in three physical states: Solid, Liquid, and Gas. The differences between them arise from how closely packed the particles are and how strongly they attract each other.
| Property | 🪨 Solid | 💧 Liquid | 💨 Gas |
| Shape | Definite (fixed) | Takes shape of container | Fills entire container |
| Volume | Definite (fixed) | Definite (fixed) | Not fixed; expands |
| Compressibility | Very low (negligible) | Very low | Highly compressible |
| Fluidity | Cannot flow (rigid) | Flows easily (fluid) | Flows very easily |
| Interparticle Space | Minimum | Intermediate | Maximum |
| Force of Attraction | Maximum | Intermediate | Minimum |
| Kinetic Energy | Minimum | Intermediate | Maximum |
| Particle Arrangement | Highly ordered | Layers slide over each other | Random, disordered |
| Density | Generally highest | Intermediate | Lowest |
| Examples | Iron, wood, ice, stone | Water, milk, juice, oil | Air, steam, LPG, oxygen |
|
5. Particle Arrangement Diagrams |
The diagrams below represent how particles are arranged in each state. Each coloured circle represents one particle of matter.
|
🪨 Solid Tightly packed, ordered rows Particles vibrate in fixed positions. Cannot flow or be compressed. |
💧 Liquid Close but with some gaps Particles slide over each other. Can flow; takes shape of container. |
💨 Gas Far apart, random positions Particles move randomly at high speed. Highly compressible. |
Fig. 2 — Particle arrangement in solids, liquids and gases. Larger gaps = more freedom of movement.
|
6. Change of State |
Matter does not stay locked in one state forever. By changing temperature or pressure, we can convert matter from one state to another. Water is the perfect example — it exists as ice (solid), liquid water, and steam (gas).
|
Melting (Fusion) Solid → Liquid. Achieved by heating. The temperature at which this happens (at atmospheric pressure) is the melting point. For ice: 273.15 K (0°C). |
Solidification (Freezing) Liquid → Solid. Achieved by cooling. Particles slow down until they lock into fixed positions. Water freezes at 273 K (0°C). |
|
Vaporisation / Boiling Liquid → Gas. The boiling point is the temperature at which a liquid converts to gas throughout its bulk (not just at the surface). For water: 373 K (100°C). |
Condensation Gas → Liquid. Achieved by cooling or increasing pressure. Water droplets on a cold glass surface are condensed water vapour from the air. |
|
Sublimation Solid → Gas (directly, skipping liquid). Examples: camphor, naphthalene balls, dry ice (solid CO₂) at normal pressure. |
Deposition Gas → Solid (directly, skipping liquid). The reverse of sublimation. Example: frost forming on cold surfaces from water vapour. |
▶ Diagram 2 — Interconversion of States of Matter
|
SOLID e.g. Ice |
Melting / Fusion → ← Solidification |
LIQUID e.g. Water |
Vaporisation → ← Condensation |
|
⇧ Deposition Sublimation ⇩ |
GAS (e.g. Steam) background colour: #ea580c |
|
Sublimation: Solid → Gas Deposition: Gas → Solid |
(both bypass liquid state) |
GAS e.g. Steam / Air |
Fig. 3 — All six state changes shown. Heating provides energy; cooling removes it.
💡 Latent Heat — Why Temperature Stays Constant During Change of State
When you heat ice at 0°C, the temperature does not rise immediately. Instead, heat energy is used to break the forces of attraction between particles. This “hidden” heat is called latent heat.
| Type | Full Name | Definition |
| Latent Heat of Fusion | Heat absorbed while melting | Energy needed to change 1 kg of solid into liquid at its melting point, without any rise in temperature. |
| Latent Heat of Vaporisation | Heat absorbed while boiling | Energy needed to change 1 kg of liquid into gas at its boiling point, without any rise in temperature. |
⛀ Temperature Scale Conversion
| Kelvin (SI Unit) | Celsius |
| K = °C + 273 | °C = K − 273 |
| 273 K = 0°C (melting point of ice) | 373 K = 100°C (boiling point of water) |
|
7. Evaporation |
Evaporation is the conversion of a liquid to vapour at a temperature below its boiling point. It is a surface phenomenon — only particles at the surface of the liquid, which have higher-than-average kinetic energy, escape into the atmosphere. Boiling, by contrast, occurs throughout the bulk of the liquid.
Factors That Increase the Rate of Evaporation
| Factor | Effect on Evaporation | Real-Life Example |
| ↑ Surface Area | Rate increases — more particles exposed to air | Spreading wet clothes on a line dries them faster than leaving them bunched up |
| ↑ Temperature | Rate increases — more particles gain enough energy to escape | Puddles dry faster on a hot sunny day than a cold day |
| ↓ Humidity | Rate increases — less water vapour in air, so more can enter | Clothes dry faster on a dry day than a humid monsoon day |
| ↑ Wind Speed | Rate increases — water vapour is carried away, making room for more | Clothes dry faster on a windy day |
❄ Why Evaporation Causes Cooling
When liquid particles evaporate, they take energy from their surroundings (or from your skin). This absorption of latent heat of vaporisation reduces the thermal energy of the remaining liquid and the surrounding surface — making them feel cold.
Examples: Acetone (nail polish remover) on your palm feels cool. Earthen pots (matka) keep water cool because water seeps through tiny pores and evaporates, cooling the remaining water. We sweat to cool our bodies — sweat evaporates, carrying heat away from the skin.
|
8. Worked Examples |
Example 1
Q: Convert 300 K and 573 K to the Celsius scale.
▶ Show Solution
Formula: °C = K − 273
300 K → 300 − 273 = 27°C
573 K → 573 − 273 = 300°C
Example 2
Q: What is the physical state of water at 250°C and at 100°C?
▶ Show Solution
Water boils at 100°C = 373 K.
At 250°C: Well above boiling point → Water is in gaseous state (steam/water vapour).
At 100°C: Exactly at boiling point → Both liquid and gaseous states coexist (water is changing into steam). In practice, at exactly 100°C at 1 atm, water is at its boiling point — considered liquid turning to gas.
Example 3
Q: Why does the smell of hot sizzling food reach you several metres away, but to smell cold food you need to go close?
▶ Show Solution
The aroma of food consists of gas particles that diffuse into the surrounding air. At higher temperatures, the kinetic energy of these particles increases significantly, causing them to move faster and spread (diffuse) over larger distances in less time. Cold food has slower-moving aroma particles that cannot travel far before settling — so you must get close to detect them.
Example 4
Q: Why is ice at 273 K more effective in cooling a drink than water at the same temperature?
▶ Show Solution
Ice at 273 K must first absorb the latent heat of fusion (334 kJ/kg) to melt before it can begin absorbing further heat from the drink. Water at 273 K has already received this latent heat. Therefore, ice absorbs far more energy from its surroundings (your drink) than the same mass of cold water at the same temperature — making it a much more effective coolant.
Example 5
Q: Which produces more severe burns — boiling water (373 K) or steam at 373 K? Explain.
▶ Show Solution
Steam at 373 K causes more severe burns than boiling water at the same temperature. Although both are at 373 K, steam contains extra energy in the form of its latent heat of vaporisation. When steam touches skin, it first releases this latent heat as it condenses to water, and then the resulting hot water continues to burn the skin. Boiling water only delivers the heat from its temperature, not the additional latent heat.
Example 6
Q: Arrange these in increasing order of forces of attraction between particles: oxygen, water, sugar.
▶ Show Solution
Oxygen is a gas → minimum interparticle force. Water is a liquid → intermediate force. Sugar is a solid → maximum force.
Increasing order: Oxygen < Water < Sugar
Example 7
Q: Why does naphthalene (mothball) disappear over time without leaving any solid residue?
▶ Show Solution
Naphthalene undergoes sublimation — it converts directly from solid to gaseous state at room temperature without passing through the liquid state. This is why the solid simply disappears over time with no liquid residue left behind.
Example 8
Q: A diver cuts through water in a swimming pool. Which property of matter does this show?
▶ Show Solution
This demonstrates that particles of matter have spaces between them. The diver’s body pushes water particles aside, occupying those spaces and moving through the water. It also shows that the interparticle force of attraction in liquids is not so strong as to prevent movement through them — liquids have fluidity.
Example 9
Q: Why does a desert cooler work better on a hot, dry day than on a humid day?
▶ Show Solution
A desert cooler works by blowing air over wet pads so that water evaporates, cooling the air. On a hot, dry day, the humidity is low, meaning the surrounding air can absorb a large amount of water vapour. This allows rapid evaporation from the pads, which absorbs more latent heat and produces greater cooling. On a humid day, the air is already saturated with water vapour — evaporation slows dramatically, reducing the cooling effect.
Example 10
Q: Convert 25°C and 373°C to the Kelvin scale. State the physical state of water at each temperature.
▶ Show Solution
Formula: K = °C + 273
25°C → 25 + 273 = 298 K → Water is a liquid (between 273 K and 373 K).
373°C → 373 + 273 = 646 K → Far above boiling point (373 K) → Water is in the gaseous state (steam).
|
9. Practice Sets A – D |
📝 Chapter Summary
|
Matter & Particles Matter = mass + volume. Made of tiny particles with spaces between them. Particles are always moving (kinetic energy) and attract each other. |
Three States Solid: rigid, fixed shape & volume. Liquid: flows, fixed volume. Gas: fills container, highly compressible. Differences arise from interparticle space and attraction. |
|
Change of State Changed by temperature or pressure. Melting (273 K), Boiling (373 K). Latent heat absorbed/released without temperature change. Sublimation: solid→gas. Deposition: gas→solid. |
Evaporation Surface phenomenon below boiling point. Increases with: more surface area, higher temp, lower humidity, higher wind speed. Absorbs latent heat → causes cooling. |
|
Key Quantities & Units
|
|
⚡ 8-Point Exam Quick-Check |
| 1 | Matter is anything with mass and volume. Thoughts, love, and cold are NOT matter. |
| 2 | Particles of matter have spaces between them, are continuously moving, and attract each other. |
| 3 | Diffusion is the spontaneous mixing of particles. Rate: Gas > Liquid > Solid. Heating speeds it up. |
| 4 | Solids: rigid, fixed shape & volume. Liquids: fluid, fixed volume. Gases: fluid, fill container, compressible. |
| 5 | Melting point of ice = 273 K (0°C). Boiling point of water = 373 K (100°C). K = °C + 273. |
| 6 | Latent heat: energy absorbed/released during a change of state without changing temperature. Fusion = melting; Vaporisation = boiling. |
| 7 | Sublimation = solid → gas directly (camphor, naphthalene, dry ice). Deposition = gas → solid directly (frost). |
| 8 | Evaporation causes cooling because particles absorb latent heat of vaporisation from surroundings. Rate ↑ with surface area, temperature, wind speed; Rate ↓ with high humidity. |
This comprehensive revision guide on Matter in Our Surroundings covers all key topics for Grade 9 Science including the definition of matter, physical and chemical classification, characteristics of particles of matter (interparticle spaces, diffusion, and forces of attraction), states of matter (solid, liquid and gas), comparison of all three states, change of state through melting, freezing, boiling, condensation, sublimation and deposition, the concept of latent heat of fusion and vaporisation, the Kelvin temperature scale, and evaporation with its cooling effect. Worked examples, practice sets, and exam quick-checks are designed to help students prepare for school tests and competitive examinations. Visit School Revise for chapter-wise notes, diagrams, and practice questions across all Grade 9 subjects.