Class 8 Science Chapter 8 – Nature of Matter: Elements, Compounds, and Mixtures from NCERT Curiosity with easy Notes and complete Book Solutions. Get simple explanations, important concepts, questions and answers, and revision material for effective learning, practice and exam preparation.
Nature of Matter: Elements, Compounds, and Mixtures
Curiosity — Textbook of Science for Grade 8
Chapter 8 | Easy Notes, Concepts, Book Questions & Solutions
Chapter at a Glance
Mixture
A mixture contains two or more substances. The substances keep their own properties and do not chemically react with each other.
Components
The individual substances present in a mixture are called its components.
Uniform Mixture
The components are evenly distributed and cannot be distinguished separately.
Examples: sugar solution, air, vinegar.
Non-uniform Mixture
The components are not evenly distributed and can generally be seen separately.
Examples: sprout salad, sand and water, oil and water.
Pure Substance
A pure substance contains only one type of substance and consists of the same type of particles.
Pure substances are of two types: elements and compounds.
Element
An element is a pure substance that cannot be broken down into simpler substances.
Examples: iron, gold, oxygen, sulfur, carbon.
Compound
A compound is formed when two or more different elements combine chemically in a fixed ratio.
Examples: water, sodium chloride, sugar, iron sulfide.
Minerals
Minerals are natural solid substances found on Earth with a fixed chemical composition. Most minerals are compounds, while some are pure elements.
8.1 What Are Mixtures?
| Type | Meaning | Examples |
|---|---|---|
| Uniform mixture | Components are evenly distributed. | Air, sugar water, vinegar |
| Non-uniform mixture | Components are not evenly distributed. | Sprout salad, sand and water, oil and water |
Our scientific heritage
Mishraloha was the name given to mixtures of two or more metals having properties different from their constituent metals.
Bronze is an alloy of copper and tin.
8.1.1 Is air a mixture?
Nitrogen makes up about 78% of air.
Oxygen supports respiration and combustion.
Air also contains water vapour and carbon dioxide.
Activity 8.1: Let us experiment
Calcium oxide reacts with water to form calcium hydroxide and releases heat.
Lime water turns milky when carbon dioxide reacts with calcium hydroxide.
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Activity 8.2: Let us explore
A black sheet kept near an open window or in a garden may collect tiny dust particles.
This shows that dust particles are suspended in air.
A step further
Major air pollutants include particulate matter such as dust and soot and gases such as carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide.
AQI means Air Quality Index. It describes the quality of air.
8.1.2 Types of mixtures
| S.No. | Mixture-type | Examples | Uniform or non-uniform |
|---|---|---|---|
| 1 | Gas and gas | Air | Uniform |
| 2 | Gas and liquid | Aerated water, oxygen dissolved in water | Uniform |
| 3 | Solid and gas | Carbon particles in air | Non-uniform |
| 4 | Liquid and liquid | Vinegar, oil and water | Vinegar – Uniform; Oil and water – Non-uniform |
| 5 | Solid and liquid | Sand and water, seawater | Sand and water – Non-uniform; Seawater – Uniform |
| 6 | Solid and solid | Baking powder, alloys | Generally uniform when components are evenly mixed |
8.2 What Are Pure Substances?
Pure does not always mean the same thing in daily life and science.
In daily life, “pure” usually means that a product is not adulterated.
In science, a pure substance contains only one type of substance.
Milk – mixture
Packed fruit juice – mixture
Baking soda – pure substance
Sugar – pure substance
Soil – mixture
8.3 What Are the Types of Pure Substances?
Water can change into ice or vapour by physical changes. In these changes, the particles of water remain the same.
But passing electricity through water produces hydrogen and oxygen. This shows that water contains two different elements.
Activity 8.3: Let us experiment
Electricity is passed through water containing a few drops of dilute sulfuric acid.
Gas bubbles form at both terminals.
Two gases are collected and tested.
Water is therefore made from two different elements.
8.3.1 Elements
Examples: gold, silver, sulfur, carbon, hydrogen, oxygen, iron and aluminium.
Atoms and molecules
Each element is made up of identical particles called atoms.
Some atoms join together to form molecules.
Two hydrogen atoms form one hydrogen molecule. Two oxygen atoms form one oxygen molecule.
Elements can be classified as:
- Metals: gold, silver, magnesium, iron, aluminium
- Non-metals: carbon, sulfur, hydrogen, oxygen
- Metalloids: silicon and boron have intermediate properties
8.3.2 Compounds
The properties of a compound are different from the properties of the elements that form it.
For water, hydrogen and oxygen combine in a fixed ratio of 2:1.
Activity 8.4: Let us experiment
When sugar is heated, it first turns brown and later becomes blackish.
Water droplets appear and carbon remains behind.
Sugar decomposes into carbon and water, so sugar is a compound.
A step further
More than 45 different elements are used in manufacturing a mobile phone, including elements used in its screen, battery and other components.
Activity 8.5: Let us experiment
Iron filings and sulfur powder are first mixed to make Sample A.
The mixture is then heated to form a black mass called Sample B.
Sample A
Sample A is a mixture of iron and sulfur.
Iron keeps its magnetic property and can be separated from sulfur using a magnet.
Sample B
Sample B is iron sulfide, a compound.
Iron and sulfur have chemically combined and cannot be separated using a magnet.
8.4 How Do We Use Elements, Compounds, and Mixtures?
Elements, compounds and mixtures are used everywhere around us.
Air is a mixture.
Water is a compound.
Iron and aluminium are elements used in construction and vehicles.
Stainless steel is an alloy and therefore a mixture.
Wood, steel and concrete are mixtures used as building materials.
Graphene aerogel
Graphene aerogel is made from carbon. It is highly porous and can absorb materials, so it has potential uses in cleaning oil spills and in energy-saving devices.
8.5 What Are Minerals?
Most rocks are mixtures of minerals.
Some minerals are pure elements, such as gold, silver, copper, sulfur and carbon.
Most minerals are compounds made of more than one element.
| Mineral | Example use or importance |
|---|---|
| Quartz | Used in many materials and industries |
| Calcite | Used in making cement |
| Mica | Used in electrical and other applications |
| Talc | Used to make talcum powder |
Our scientific heritage – Dhokra art
Dhokra art uses metals such as brass or bronze. A wax model is covered with clay, the wax is removed by heating, and molten metal is poured into the hollow mould.
Snapshots – Quick Revision
- A mixture consists of two or more substances mixed together.
- The substances in a mixture retain their individual properties.
- The substances forming a mixture are called its components.
- A pure substance consists of the same type of particles.
- A pure substance can be an element or a compound.
- Elements are the simplest substances and are building blocks of matter.
- Compounds contain two or more elements chemically combined in a fixed ratio.
- The properties of a compound are different from the properties of its constituent elements.
- Minerals are natural solid substances with a fixed chemical composition.
- Most minerals are compounds, while some are pure elements.
Keep the Curiosity Alive – Book Questions
A and B, combine to form a product C:
A + B C
Assume that A and B cannot be broken down into simpler substances by chemical reactions. Based on this information, which of the following statements is correct?
(i) A, B, and C are all compounds and only C has a fixed composition.
(ii) C is a compound, and A and B have a fixed composition.
(iii) A and B are compounds, and C has a fixed composition.
(iv) A and B are elements, C is a compound, and has a fixed composition.
Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.
(i) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.
(iii) Assertion is true, but Reason is false.
(iv) Assertion is false, but Reason is true.
(i) Elements — water, nitrogen, iron, air.
(ii) Uniform mixtures— minerals, seawater, bronze, air.
(iii) Pure substances— carbon dioxide, iron, oxygen, sugar.
(iv) Non-uniform mixtures — air, sand, brass, muddy water.
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Why?
When?
How long?
Where? Why not?
Carbon dioxide, sand, seawater, magnesium oxide, muddy water, aluminium, gold, oxygen, rust, iron sulfide, glucose, air, water, fruit juice, nitrogen, sodium chloride, sulfur, hydrogen, baking soda.
Elements Compounds Mixtures
Table 8.3
Identify pure substances amongst these and list them below.
Pure substances
Elements: aluminium, gold, oxygen, nitrogen, sulfur, hydrogen.
Compounds: carbon dioxide, magnesium oxide, rust, iron sulfide, glucose, water, sodium chloride, baking soda.
Mixtures: sand, seawater, muddy water, air, fruit juice.
Pure substances: all the elements and compounds listed above.
Word equation: Iron + Sulfur → Iron sulfide
Word equation: Iron + Dilute Hydrochloric Acid → Iron Chloride + Hydrogen gas
Water: drinking, washing.
Carbon dioxide: used in fire extinguishers, used by plants during photosynthesis.
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I think …
But we thought … Maybe …
Shouldn’t it be …
Discover, Design, and Debate
z Design and create comic strips from real-life examples to differentiate between elements, compounds, and mixtures with diagrams and illustrate their properties and uses.
Easy idea: Show an element as one type of particle, a compound as different particles chemically joined, and a mixture as different particles together but not chemically joined.
z Search for discoveries of some elements (such as phosphorus, sodium), compounds (such as penicillin) and mixtures (such as brass, bronze, stainless steel). Present your findings in the class.
Easy idea: Prepare a small chart showing the substance, who discovered it or developed it, its type and its use.
z Let us search: Read labels on items like detergents or snacks, and try to list the mixtures and compounds they contain.
Easy idea: Read the ingredients carefully and classify the substances you can identify.
z Work in groups: Each group will pretend to be in the role of either an element, a compound, or a mixture. Debate which category among them is the most important.
Easy idea: Explain how your assigned category is useful in daily life. Remember that all three categories are important.
Quick Comparison
| Feature | Element | Compound | Mixture |
|---|---|---|---|
| Made of | One type of element | Two or more elements | Two or more substances |
| Combination | Not chemically combined with another element | Chemically combined | Not chemically combined |
| Composition | Fixed | Fixed ratio | May vary |
| Can physical methods separate components? | No | No | Usually yes |
| Example | Iron | Water | Air |
Prepare with this NCERT Curiosity worksheet for Chapter 8. The worksheet includes important questions and revision exercises to help students understand key concepts, practise what they have learned, and prepare effectively for class tests and exams.
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