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.

• 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

Written by Satish

NCERTBooks.org is an independent educational resource run by a small team focused on making official NCERT textbooks easy to find, read, and download for students, parents, and teachers across India. We are not affiliated with NCERT or the Ministry of Education -- we organise publicly available NCERT content by class and subject, verify links against official sources, and build tools (like our in-browser reader) that make studying more convenient. Every guide we publish is written and reviewed by our team based on the actual NCERT curriculum and syllabus.