IGCSE Solids, Liquids and Gases: Complete Guide for Cambridge IGCSE Chemistry

IGCSE solids, liquids and gases are fundamental topics in Cambridge IGCSE Chemistry that form the foundation for understanding matter and its properties. Mastering states of matter, particle theory, and phase changes is essential for achieving top grades in IGCSE Chemistry exams.

This comprehensive IGCSE solids, liquids and gases guide covers everything you need to know, including the properties of each state of matter, particle arrangement and behavior, phase transitions, kinetic theory, step-by-step worked examples, common exam questions, and expert tips from Tutopiya’s IGCSE chemistry tutors. We’ll also show you how to avoid the most common mistakes that cost students valuable marks.

🎯 What you’ll learn: By the end of this guide, you’ll know how to describe the properties of solids, liquids, and gases, explain particle behavior in each state, understand phase changes, and apply these concepts to solve problems in IGCSE Chemistry exams.

Already studying with Tutopiya? Practice these skills with our dedicated IGCSE Chemistry practice deck featuring exam-style questions and instant feedback.

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Why IGCSE Solids, Liquids and Gases Matter

IGCSE solids, liquids and gases are essential topics that appear throughout the IGCSE Chemistry curriculum. Here’s why they’re so important:

• Foundation topic: Required for understanding all other chemistry concepts including bonding, reactions, and thermodynamics
• High frequency: Questions about states of matter appear in almost every IGCSE chemistry paper
• Exam weight: Typically worth 6-10 marks per paper
• Real-world applications: Essential for understanding everyday phenomena and industrial processes
• Link to other topics: Connects to diffusion, bonding, energy changes, and physical properties

Key insight from examiners: Students often confuse the properties of different states or struggle with particle diagrams. This guide will help you master these concepts systematically.

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Understanding the Three States of Matter

Matter exists in three main states: solid, liquid, and gas. These states differ in how particles are arranged and how they move.

States of Matter Overview

State	Particle Arrangement	Particle Movement	Shape	Volume
Solid	Closely packed, regular pattern	Vibrate about fixed positions	Fixed	Fixed
Liquid	Closely packed, irregular arrangement	Move around each other	Not fixed (takes container shape)	Fixed
Gas	Widely spaced, random arrangement	Move rapidly in all directions	Not fixed	Not fixed (fills container)

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Properties of Solids

Solids have the following key properties:

Particle Arrangement

• Particles are closely packed together
• Arranged in a regular pattern (crystalline structure)
• Strong forces of attraction between particles
• Particles can only vibrate about fixed positions

Physical Properties

• Fixed shape - maintains its shape
• Fixed volume - volume doesn’t change easily
• Cannot be compressed - particles are already close together
• High density - particles are closely packed
• Does not flow - particles cannot move past each other

Examples

• Ice (solid water)
• Salt (sodium chloride)
• Diamond
• Iron
• Sugar

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Properties of Liquids

Liquids have the following key properties:

Particle Arrangement

• Particles are closely packed but in an irregular arrangement
• Forces of attraction are weaker than in solids
• Particles can move around each other
• Particles have more kinetic energy than in solids

Physical Properties

• No fixed shape - takes the shape of its container
• Fixed volume - volume remains constant (at constant temperature and pressure)
• Cannot be easily compressed - particles are still close together
• Moderate density - between solids and gases
• Can flow - particles can move past each other

Examples

• Water
• Ethanol
• Mercury
• Oil
• Milk

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Properties of Gases

Gases have the following key properties:

Particle Arrangement

• Particles are widely spaced and in a random arrangement
• Very weak forces of attraction between particles
• Particles move rapidly in all directions
• Particles have high kinetic energy

Physical Properties

• No fixed shape - takes the shape of its container
• No fixed volume - expands to fill available space
• Can be compressed - particles are far apart with space between them
• Low density - particles are widely spaced
• Can flow - particles move freely

Examples

• Oxygen
• Carbon dioxide
• Nitrogen
• Hydrogen
• Steam (water vapor)

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Particle Theory: Explaining States of Matter

Particle theory explains the properties of matter in terms of tiny particles and their behavior.

Key Principles of Particle Theory

1. All matter is made up of tiny particles (atoms, molecules, or ions)
2. Particles are in constant motion - the amount of movement depends on temperature
3. There are forces of attraction between particles
4. Particles have space between them
5. Adding energy increases particle movement
6. Removing energy decreases particle movement

Particle Diagrams

Drawing particle diagrams helps visualize states of matter:

Solid:

● ● ● ●
● ● ● ●
● ● ● ●
(Closely packed, regular pattern)

Liquid:

●   ● ●
  ●   ●
●   ●
(Irregular arrangement, can move)

Gas:

●     ●
    ●
  ●     ●
(Widely spaced, random)

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Phase Changes (Changes of State)

Matter can change from one state to another when energy is added or removed.

Heating: Solid → Liquid → Gas

Melting (Solid → Liquid)

• Process: Heating a solid increases particle energy
• Particles: Start moving more, breaking free from fixed positions
• Temperature: Melting point (specific for each substance)
• Energy: Energy is absorbed (endothermic)
• Example: Ice melting to water at 0°C

Evaporation/Boiling (Liquid → Gas)

• Process: Further heating increases particle energy more
• Particles: Move so fast they escape the liquid surface
• Temperature: Boiling point (specific for each substance)
• Energy: Energy is absorbed (endothermic)
• Example: Water boiling to steam at 100°C

Cooling: Gas → Liquid → Solid

Condensation (Gas → Liquid)

• Process: Cooling decreases particle energy
• Particles: Slow down and come closer together
• Temperature: Condensation point (same as boiling point)
• Energy: Energy is released (exothermic)
• Example: Steam condensing to water

Freezing (Liquid → Solid)

• Process: Further cooling decreases particle energy more
• Particles: Slow down enough to form a regular pattern
• Temperature: Freezing point (same as melting point)
• Energy: Energy is released (exothermic)
• Example: Water freezing to ice at 0°C

Sublimation and Deposition

Sublimation (Solid → Gas directly)

• Example: Dry ice (solid CO₂) → Carbon dioxide gas
• Example: Iodine crystals → Iodine vapor

Deposition (Gas → Solid directly)

• Example: Water vapor → Frost on windows

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Heating and Cooling Curves

Heating curves show temperature changes when a substance is heated at a constant rate.

Key Features of a Heating Curve

1. Solid phase: Temperature increases steadily
2. Melting point: Temperature stays constant (energy used to break bonds)
3. Liquid phase: Temperature increases steadily
4. Boiling point: Temperature stays constant (energy used to overcome attractions)
5. Gas phase: Temperature increases steadily

Cooling Curve

A cooling curve shows the reverse process when a substance is cooled.

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Kinetic Theory and Energy

Kinetic theory explains the behavior of particles in terms of their motion and energy.

Key Concepts

• Kinetic energy: Energy due to motion
• Temperature: Measure of average kinetic energy of particles
• Higher temperature: Particles move faster, have more kinetic energy
• Lower temperature: Particles move slower, have less kinetic energy

Particle Movement

In Solids:

• Particles vibrate in fixed positions
• Low kinetic energy
• Strong forces hold particles together

In Liquids:

• Particles move around each other
• Moderate kinetic energy
• Moderate forces between particles

In Gases:

• Particles move rapidly in all directions
• High kinetic energy
• Weak forces between particles

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Pressure in Gases

Pressure in gases is caused by particles colliding with the container walls.

Factors Affecting Gas Pressure

1. Temperature

• Increase temperature: Particles move faster, collide more frequently and with more force → Pressure increases
• Decrease temperature: Particles move slower, fewer collisions → Pressure decreases

2. Volume

• Decrease volume: Particles are closer together, more collisions → Pressure increases
• Increase volume: Particles are farther apart, fewer collisions → Pressure decreases

3. Number of Particles

• More particles: More collisions → Pressure increases
• Fewer particles: Fewer collisions → Pressure decreases

Boyle’s Law (Volume and Pressure)

At constant temperature: Volume × Pressure = Constant

If volume decreases, pressure increases (and vice versa).

Example: If you halve the volume, pressure doubles.

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Diffusion

Diffusion is the movement of particles from an area of high concentration to an area of low concentration.

Diffusion in Different States

Gases: Very fast diffusion (particles move rapidly)

• Example: Smell of perfume spreading through a room

Liquids: Slower diffusion (particles move slower)

• Example: Food coloring mixing in water

Solids: Very slow diffusion (particles can only vibrate)

• Example: Diffusion at high temperatures only

Factors Affecting Diffusion Rate

1. Temperature: Higher temperature → faster diffusion
2. Particle size: Smaller particles → faster diffusion
3. State of matter: Gases > Liquids > Solids

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Step-by-Step Method for States of Matter Problems

1. Identify the state(s) involved in the question
2. Recall the properties of that state
3. Consider particle arrangement and movement
4. Apply particle theory to explain observations
5. Use diagrams if helpful
6. Check your answer - does it make sense?

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Worked Examples

Example 1: Describing Properties

Explain why a solid has a fixed shape but a liquid does not.

Solution:

• Solid: Particles are closely packed in a regular pattern and held in fixed positions by strong forces. They can only vibrate, so the shape remains fixed.
• Liquid: Particles are closely packed but can move around each other. They have enough energy to overcome some of the forces, so they flow and take the shape of the container.

Example 2: Phase Change

Describe what happens when ice is heated from -10°C to 110°C.

Solution:

1. -10°C to 0°C (Solid phase): Temperature increases, particles vibrate more, but ice remains solid.
2. At 0°C (Melting): Temperature stays constant while ice melts to water. Energy is used to break bonds between particles.
3. 0°C to 100°C (Liquid phase): Temperature increases, particles move faster, but water remains liquid.
4. At 100°C (Boiling): Temperature stays constant while water boils to steam. Energy is used to overcome attractions.
5. Above 100°C (Gas phase): Temperature increases, steam particles move very rapidly.

Example 3: Explaining Diffusion

Why does diffusion occur faster in gases than in liquids?

Solution: In gases, particles have high kinetic energy and move rapidly in all directions with large spaces between them. In liquids, particles have less kinetic energy, move slower, and are closer together. Therefore, gas particles spread out much faster than liquid particles.

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Common Examiner Traps (and How to Dodge Them)

• Confusing particle arrangement - Solids have regular patterns; liquids and gases have irregular arrangements
• Forgetting about forces - Always mention forces of attraction when explaining properties
• Phase change temperatures - Remember temperature stays constant during phase changes
• Particle movement - Solids vibrate; liquids move around; gases move rapidly
• Compressibility - Only gases can be easily compressed; solids and liquids cannot
• Density order - Generally: Solid > Liquid > Gas

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IGCSE Solids, Liquids and Gases Practice Questions

Question 1: Properties

State three differences between the properties of a solid and a gas.

Solution:

1. Solids have fixed shape; gases have no fixed shape
2. Solids cannot be compressed; gases can be compressed
3. Solids have high density; gases have low density

Question 2: Particle Arrangement

Draw particle diagrams to show the arrangement of particles in a solid and a gas.

Solution:

• Solid: Closely packed particles in regular pattern
• Gas: Widely spaced particles in random arrangement

Question 3: Phase Changes

Explain why the temperature stays constant when ice is melting, even though heat is being added.

Solution: The energy added is used to break the bonds between particles and overcome the forces holding them in the solid structure, rather than increasing the kinetic energy (temperature) of the particles. Once all the ice has melted, the temperature begins to rise again.

Question 4: Diffusion

Explain why diffusion is faster in gases than in liquids.

Solution: Gas particles have higher kinetic energy and move much faster than liquid particles. They are also much farther apart, allowing them to spread out more easily. Liquid particles have lower kinetic energy, move slower, and are closer together, making diffusion slower.

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Frequently Asked Questions About IGCSE Solids, Liquids and Gases

What are the three states of matter?

The three states of matter are solid, liquid, and gas. They differ in particle arrangement, movement, and properties.

Why do solids have a fixed shape?

Solids have a fixed shape because particles are closely packed in a regular pattern and held in fixed positions by strong forces. They can only vibrate, not move around.

Why can gases be compressed but solids cannot?

Gases have widely spaced particles with lots of space between them, so they can be pushed closer together. Solids have closely packed particles with little space, so they cannot be compressed.

What happens during melting?

During melting, a solid changes to a liquid. Energy is added to break the bonds between particles, allowing them to move around each other. The temperature stays constant during this process.

What is diffusion?

Diffusion is the movement of particles from an area of high concentration to an area of low concentration. It occurs fastest in gases and slowest in solids.

Why does temperature stay constant during phase changes?

The energy added (or removed) is used to break (or form) bonds between particles rather than change their kinetic energy (temperature). Once the phase change is complete, temperature changes again.

What is the difference between evaporation and boiling?

Evaporation occurs at the surface of a liquid at any temperature. Boiling occurs throughout the liquid at a specific temperature (boiling point).

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Related IGCSE Chemistry Resources

Strengthen your IGCSE Chemistry preparation with these comprehensive guides:

• IGCSE Diffusion: Complete Guide - Master diffusion and particle movement
• IGCSE Elements, Compounds and Mixtures: Complete Guide - Master classification of matter
• IGCSE Chemistry Revision Notes, Syllabus and Preparation Tips - Complete syllabus overview, topic breakdown, and revision strategies
• IGCSE Past Papers Guide - Access free IGCSE past papers and exam resources

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