NCERT Class 8 Science Chapter 8
Nature of Matter: Elements, Compounds, and Mixtures
NCERT Class 8 Science Chapter 8 introduces students to the classification of matter into elements, compounds, and mixtures — a fundamental concept in CBSE chemistry. Students learn how elements combine to form compounds with entirely new properties, and how mixtures differ from compounds in that they retain the properties of their constituents. Separation techniques and chemical versus physical changes are also covered.
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Key Terms
- Element
- A pure substance made of only one kind of atom that cannot be broken down into simpler substances by chemical means; e.g., oxygen, iron, gold.
- Compound
- A pure substance formed when two or more elements combine chemically in a fixed ratio; has different properties from its constituent elements; e.g., water (H₂O), salt (NaCl).
- Mixture
- A combination of two or more substances that are not chemically combined; each substance retains its own properties and can be separated by physical methods.
- Homogeneous Mixture
- A mixture with uniform composition throughout, where the components cannot be distinguished; e.g., salt dissolved in water (saline solution).
- Heterogeneous Mixture
- A mixture with non-uniform composition where the components can be seen as separate phases; e.g., sand and water, oil and water.
- Chemical Change
- A change in which new substances with different properties are formed; generally irreversible; e.g., burning wood, rusting of iron.
- Physical Change
- A change in which no new substance is formed; the original substance can usually be recovered; e.g., melting ice, dissolving salt.
Frequently Asked Questions
What is the difference between elements and compounds Class 8?▾
An element is a pure substance made of only one type of atom (e.g., oxygen, carbon, gold) and cannot be broken down chemically. A compound is formed when two or more elements combine chemically in a fixed ratio (e.g., water H₂O is made of hydrogen and oxygen). Compounds have completely different properties from their constituent elements.
What is the difference between a mixture and a compound Class 8 Science?▾
A mixture is a physical combination where substances retain their own properties and can be separated by physical methods (e.g., filtration, evaporation). A compound forms through a chemical reaction; its components are in a fixed ratio and cannot be separated by physical methods. Mixtures have variable composition; compounds have a fixed composition.
What are examples of elements, compounds, and mixtures Class 8?▾
Elements: oxygen (O), iron (Fe), gold (Au), carbon (C). Compounds: water (H₂O), common salt (NaCl), carbon dioxide (CO₂), sugar (C₁₂H₂₂O₁₁). Mixtures: air (mixture of gases), seawater (salt in water), soil (various minerals and organic matter), alloys (like brass — copper and zinc).
What is the difference between physical and chemical change Class 8 NCERT?▾
A physical change does not produce a new substance — the change is reversible and only affects form or state (e.g., melting ice, tearing paper). A chemical change produces one or more new substances with different properties and is usually irreversible (e.g., burning wood, rusting iron, cooking food).
How can mixtures be separated Class 8?▾
Mixtures can be separated using physical methods based on differences in physical properties: filtration (solid from liquid), evaporation (dissolved solid from liquid), distillation (two liquids with different boiling points), magnetic separation (magnetic material from non-magnetic), and chromatography (substances with different solubilities).
Why does water have different properties from hydrogen and oxygen Class 8?▾
Water (H₂O) is a compound formed when hydrogen and oxygen react chemically. In this chemical combination, the atoms share electrons and form new bonds, creating a new substance with completely different properties. Hydrogen is a flammable gas, oxygen supports combustion, but water (their compound) actually extinguishes fire — demonstrating that compounds differ from their elements.
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