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

Condensed revision notes for Class 8 Science Chapter 8: Nature of Matter – Elements, Compounds and Mixtures (Curiosity). These Class 8 Science Chapter 8 notes are ideal for quick revision just before exams.

Last Updated: September 23, 2026

• Matter: anything with mass that occupies space (light, heat and sound are forms of energy, not matter).
• Pure substance: has a fixed composition throughout — includes elements and compounds only.
• Element: made of only one kind of atom; cannot be broken into simpler substances by chemical means (e.g. aluminium, gold, oxygen, nitrogen, sulphur, hydrogen).
• Compound: two or more different elements chemically combined in a fixed ratio (law of definite proportions); has properties completely different from its constituent elements; formed by chemical change; separable only by chemical methods (e.g. water, carbon dioxide, sodium chloride, magnesium oxide, iron sulphide, glucose, baking soda, rust).
• Mixture: two or more substances physically combined in variable proportions; each component keeps its own properties; separable by physical methods (filtration, evaporation, distillation, magnetic separation).
• Homogeneous (uniform) mixture: same composition throughout (air, salt solution, alloys, soda water).
• Heterogeneous (non-uniform) mixture: visibly distinct components (sand + water, muddy water, fruit salad).
• Alloys (e.g. brass = copper+zinc, steel = iron+carbon) are homogeneous mixtures of metals — NOT compounds, despite their uniform appearance.
• Test for carbon dioxide: turns lime water milky (forms calcium carbonate) — a chemical change.
• Electrolysis of water: H₂O → H₂ (cathode, “pop” test) + O₂ (anode, relights glowing splint) in a 2:1 volume ratio — proves water is a compound.
• Heating sugar: chars into carbon + water vapour, proving sugar is a compound of carbon, hydrogen and oxygen.
• Iron + sulphur: before heating = magnetic, separable mixture; after heating = iron sulphide (FeS), a non-magnetic compound that cannot be separated physically.
• Mineral: a naturally occurring substance with a definite composition in the Earth’s crust (may be an element like gold, or a compound); an ore is a mineral from which a metal can be profitably extracted.
• Key test: mixtures separate by physical methods and show variable composition; compounds require chemical methods to break down and always show fixed composition.

More on this chapter: Solutions | Extra Questions | Class 8 Science Book | Formulas/Concepts Handbook

Frequently Asked Questions

What is the difference between an element and a compound?
An element is a pure substance made of only one type of atom that cannot be broken down further by ordinary chemical means, while a compound is formed when two or more different elements combine chemically in a fixed ratio.

How is a mixture different from a compound?
In a mixture, the substances combined retain their individual properties and can be present in variable proportions, and can usually be separated by physical methods, whereas a compound has entirely new properties and needs chemical separation.

Written by Satish

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