CBSE Class 8 Science Revision Notes Chapter 8 Nature of Matter: Elements, Compounds, and Mixtures

Matter has mass and occupies space, and it may exist as a pure substance or a mixture.
Elements and compounds are pure substances, while mixtures contain two or more substances combined physically.

The air we breathe, the water we drink, the food we eat and the objects around us are made of matter. Most everyday materials contain more than one substance, while a few consist of only one type of particle.

These CBSE Class 8 Science Revision Notes Chapter 8 explain mixtures, pure substances, elements, compounds and minerals. They follow the current 2026–27 textbook and help students understand how substances are classified.

Key Takeaways

• Mixture: Two or more substances combined physically while retaining their properties.
• Pure substance: Matter made of only one type of particle.
• Element: A substance that cannot be broken into simpler substances.
• Compound: A pure substance formed when elements combine chemically in a fixed ratio.

Revise Class 8 Science Chapter 8 in 30 Minutes

First 10 minutes: Matter, mixtures, uniform and non-uniform mixtures
Next 10 minutes: Pure substances, elements, atoms and compounds
Final 10 minutes: Iron-sulfur experiment, alloys, air and minerals

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Matter in Class 8 Science Chapter 8 Notes

Matter is anything that has mass and occupies space.

Examples of matter include:

• Air
• Water
• Soil
• Wood
• Metals
• Food
• Clothes
• Books
• Plants
• Animals

All matter is made of tiny particles.

What Is Not Matter?

Some things are important in our surroundings but are not made of matter.

Examples include:

• Light
• Heat
• Electricity
• Thoughts
• Emotions

They do not have mass or occupy space in the same way as material substances.

Mixtures Class 8 Notes

A mixture is formed when two or more substances are mixed together without undergoing a chemical reaction.

The substances present in a mixture are called its components.

Main Features of a Mixture

In a mixture:

• Two or more substances are present.
• Components retain their original properties.
• Components are not chemically combined.
• Composition may vary.
• Components may often be separated by physical methods.

Everyday Examples of Mixtures

• Poha
• Sprout salad
• Lemonade
• Soup
• Sugar in water
• Salt in water
• Soil
• Air
• Stainless steel
• Brass

Components of a Mixture

The individual substances present in a mixture are called components.

For example, a sprout salad may contain:

• Green gram
• Chickpeas
• Tomato
• Onion
• Lemon juice
• Salt

Each component keeps its own identity.

Uniform and Non-Uniform Mixtures Class 8

Mixtures may be uniform or non-uniform.

Uniform Mixture

A uniform mixture has the same composition throughout.

Its components are evenly distributed and cannot be distinguished separately.

Examples include:

• Sugar solution
• Salt solution
• Air
• Vinegar
• Seawater
• Brass
• Stainless steel

Non-Uniform Mixture

A non-uniform mixture does not have the same composition throughout.

Its components may be visible with the naked eye or a magnifying device.

Examples include:

• Sprout salad
• Poha
• Sand and water
• Oil and water
• Muddy water
• Carbon particles in air

Uniform and Non-Uniform Mixture Comparison

Air as a Mixture Class 8

Air is a uniform mixture of several gases.

Its main components include:

• Nitrogen
• Oxygen
• Argon
• Carbon dioxide
• Water vapour
• Other gases in small quantities

Nitrogen forms about 78% of air.

Oxygen is needed by most living organisms for respiration and also supports combustion.

Why Is Air a Mixture?

Air is called a mixture because:

• It contains several gases.
• The gases are physically mixed.
• Each gas retains its own properties.
• The proportion of some components may change.
• The gases are not chemically bonded into one substance.

Carbon Dioxide in Air

The presence of carbon dioxide in air can be tested using lime water.

When lime water is exposed to air, it may turn milky because carbon dioxide reacts with calcium hydroxide.

The word equation is:

Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

The tiny white particles of calcium carbonate make the solution appear milky.

Dust Particles in Air

Air may also contain dust, soot and other suspended particles.

These are not permanent components of pure air. They are considered pollutants.

The number and type of dust particles vary from place to place.

Types of Mixtures

Mixtures may contain components in different physical states.

Alloys Class 8 Notes

An alloy is a uniform mixture of two or more metals, or of a metal with another substance.

Alloys often have properties different from their individual components.

Examples of Alloys

Why Are Alloys Useful?

Alloys may be:

• Stronger
• More durable
• More resistant to rust
• Easier to shape
• Suitable for utensils, buildings and machines

Stainless steel is widely used because it is strong and resists corrosion better than ordinary iron.

Pure Substances Class 8

The scientific meaning of pure is different from its everyday meaning.

Pure in Common Usage

In daily life, pure often means:

• Unadulterated
• Free from dirt
• Good quality
• Safe for use

For example, people may say pure milk or pure ghee.

Pure in Science

In science, a pure substance contains only one type of particle.

It cannot be separated into other kinds of matter by a physical process.

Examples include:

• Iron
• Oxygen
• Gold
• Water
• Common salt
• Sugar
• Carbon dioxide

A pure substance may be an element or a compound.

Mixture and Pure Substance Difference

Types of Pure Substances

Pure substances are classified into:

• Elements
• Compounds

Elements Class 8 Notes

An element is a pure substance that cannot be broken down into simpler substances.

Elements are the basic building blocks of matter.

Examples of Elements

• Hydrogen
• Oxygen
• Nitrogen
• Carbon
• Sulfur
• Iron
• Gold
• Silver
• Aluminium
• Copper

Atoms

Each element is made of identical particles called atoms.

Atoms of one element are different from atoms of another element.

For example:

• All oxygen atoms have the same basic nature.
• Hydrogen atoms are different from oxygen atoms.
• Iron atoms are different from sulfur atoms.

Molecules of Elements

Atoms of some elements do not normally exist alone.

Two or more atoms may combine to form a molecule of the same element.

Examples:

• Two hydrogen atoms form one hydrogen molecule.
• Two oxygen atoms form one oxygen molecule.

A molecule of an element contains only one kind of atom.

Classification of Elements

Elements may be classified as:

• Metals
• Non-metals
• Metalloids

Metals

Examples include:

• Iron
• Copper
• Gold
• Silver
• Aluminium
• Magnesium

Non-Metals

Examples include:

• Oxygen
• Hydrogen
• Carbon
• Sulfur
• Nitrogen

Metalloids

Some elements show properties between those of metals and non-metals.

Examples include:

• Silicon
• Boron

These are called metalloids.

Important Facts About Elements

• There are 118 known elements.
• Most elements are solids at room temperature.
• Eleven elements are gases at room temperature.
• Mercury is a liquid metal.
• Bromine is a liquid non-metal.
• Gallium and caesium melt near 30°C.

Compounds Class 8 Notes

A compound is a pure substance formed when two or more elements combine chemically in a fixed ratio.

The properties of a compound are different from the properties of the elements that form it.

Main Features of Compounds

A compound:

• Contains two or more elements.
• Has elements chemically combined.
• Has a fixed composition.
• Has new properties.
• Cannot be separated by physical methods.
• Can be broken down only through chemical processes.

Water as a Compound

Water is made of hydrogen and oxygen.

The ratio of hydrogen atoms to oxygen atoms in water is:

2:1

Water has properties completely different from hydrogen and oxygen.

• Hydrogen is a fuel.
• Oxygen supports burning.
• Water is commonly used to put out fire.

This shows that a compound has properties different from its elements.

Breaking Water into Elements

When electric current is passed through water, hydrogen and oxygen gases are produced.

Hydrogen gives a pop sound near a flame.

Oxygen makes a flame glow brighter.

This shows that water contains hydrogen and oxygen chemically combined.

Common Salt as a Compound

Common salt is sodium chloride.

It is formed from:

• Sodium
• Chlorine

Sodium is a soft, reactive metal.

Chlorine is a harmful gas.

When they combine chemically, they form sodium chloride, which has entirely different properties.

The ratio of sodium particles to chlorine particles in common salt is fixed at 1:1.

Sugar as a Compound

Sugar contains:

• Carbon
• Hydrogen
• Oxygen

When sugar is heated:

• It first turns brown.
• It later becomes black.
• Water droplets appear near the cooler part of the tube.
• Carbon remains behind.

This shows that sugar is made of more than one element and is therefore a compound.

Mixture and Compound Difference Class 8

Mixtures and compounds may both contain more than one substance or element, but they are different.

Iron and Sulfur Experiment

The iron and sulfur activity gives a clear comparison between a mixture and a compound.

Sample A: Iron and Sulfur Mixture

Iron filings and sulfur powder are mixed without heating.

In this sample:

• Iron remains iron.
• Sulfur remains sulfur.
• Iron particles can be attracted by a magnet.
• The components may be seen separately.
• Iron and sulfur can be separated.

Therefore, Sample A is a mixture.

Reaction with Hydrochloric Acid

When dilute hydrochloric acid is added to the iron and sulfur mixture:

• Iron reacts with the acid.
• Hydrogen gas is produced.
• The gas burns with a pop sound.
• Sulfur remains unchanged.

The word equation is:

Iron + Dilute hydrochloric acid → Iron chloride + Hydrogen

Sample B: Iron Sulfide Compound

When the iron and sulfur mixture is heated, a black substance forms.

This substance is iron sulfide.

In iron sulfide:

• Iron and sulfur are chemically combined.
• The substance looks uniform.
• A magnet cannot separate the iron.
• It has properties different from iron and sulfur.
• It cannot be separated physically.

Therefore, iron sulfide is a compound.

Reaction of Iron Sulfide with Acid

Iron sulfide reacts with dilute hydrochloric acid and produces hydrogen sulfide gas.

The gas has a rotten egg-like smell.

The word equation is:

Iron sulfide + Dilute hydrochloric acid → Iron chloride + Hydrogen sulfide

Iron-Sulfur Mixture and Iron Sulfide

Uses of Elements, Compounds and Mixtures

Elements, compounds and mixtures are used throughout daily life.

Uses of Elements

• Iron is used in buildings and vehicles.
• Aluminium is used in utensils and aircraft.
• Copper is used in electric wires.
• Oxygen supports respiration.
• Gold and silver are used in jewellery.

Uses of Compounds

• Water supports life.
• Sodium chloride is used as common salt.
• Medicines contain useful compounds.
• Fertilisers contain compounds needed by plants.
• Sugar provides energy.

Uses of Mixtures

• Air supports life.
• Steel is used in construction.
• Concrete is used in buildings.
• Brass and bronze are used for utensils and decorative objects.
• Wood is used in furniture and construction.

Nature of Matter Elements Compounds and Mixtures Notes

These Nature of Matter Elements Compounds and Mixtures notes can be summarised through one main classification:

Matter

Matter may be divided into:

1. Mixtures
   • Uniform mixtures
   • Non-uniform mixtures
2. Pure substances
   • Elements
   • Compounds

Minerals Class 8 Notes

Minerals are naturally occurring solid substances found in Earth.

They usually have a fixed chemical composition.

Rocks and Minerals

Most rocks are mixtures of different minerals.

Minerals may be seen:

• With the naked eye
• Through a magnifying glass
• Through a microscope

Native Minerals

Some minerals occur as pure elements.

These are called native minerals.

Examples include:

• Gold
• Silver
• Copper
• Sulfur
• Carbon

Compound Minerals

Most minerals are compounds.

Examples include:

• Quartz
• Calcite
• Mica
• Pyroxene
• Olivine
• Talc

Uses of Minerals

• Calcite is used in cement.
• Talc is used in talcum powder.
• Quartz is used in glass and electronic devices.
• Metals are extracted from mineral ores.
• Minerals are used in construction and manufacturing.

Dhokra Art and Alloys

Dhokra is a traditional metal craft associated with regions including Bihar and Odisha.

A wax model is first made and covered with clay.

After the wax is melted out, molten brass or bronze is poured into the hollow mould.

This shows how alloys are connected with traditional Indian art and craft.

Matter and Environmental Applications

Knowledge of matter helps scientists design new materials.

For example, graphene aerogel is a very light and porous material made from carbon.

Its absorbing ability may help:

• Clean oil spills.
• Develop energy-saving devices.
• Create special coatings.
• Reduce environmental pollution.

Understanding elements and compounds also helps scientists develop materials that can absorb harmful gases such as carbon dioxide.

Classification Examples Class 8 Science Chapter 8

Important Terms in CBSE Class 8 Science Chapter 8

Quick Revision of CBSE Class 8 Science Chapter 8 Notes

Use these CBSE Class 8 Science Chapter 8 notes for final revision:

• Matter has mass and occupies space.
• Light and heat are not matter.
• A mixture contains two or more substances.
• Components of a mixture retain their properties.
• Uniform mixtures have the same composition throughout.
• Non-uniform mixtures have uneven composition.
• Air is a uniform mixture of gases.
• Alloys are mixtures of metals or metals with other substances.
• A pure substance contains one type of particle.
• Elements and compounds are pure substances.
• Elements cannot be broken into simpler substances.
• Atoms are particles of elements.
• Compounds contain elements in fixed ratios.
• Water is a compound of hydrogen and oxygen.
• Sugar contains carbon, hydrogen and oxygen.
• Iron and sulfur form a mixture before heating.
• Heating iron and sulfur produces iron sulfide.
• Mixtures may be separated physically.
• Compounds require chemical methods for separation.
• Most rocks are mixtures of minerals.

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