NCERT Curiosity · Class 8 · Science
Nature of Matter: Elements, Compounds, and Mixtures
The staircase, the air, your water bottle, your clothes — almost nothing around you is made of just one substance.
Mixtures Elements Compounds Minerals
Key idea
What Are Mixtures
Non-uniform

Components stay visible, even with a magnifying glass — like a sprout salad.

Uniform

Components can't be told apart even under a microscope — like sugar dissolved in water, or an alloy.

Key idea
Air is a uniform mixture — mostly nitrogen and oxygen.
Lime water turns milky when exposed to air, proving carbon dioxide is really there.
Key idea
Types of Mixtures

Gas – Gas

Air.

Gas – Liquid

Soda water.

Solid – Gas

Dust in air.

Liquid – Liquid

Vinegar, oil + water.

Solid – Liquid

Seawater, sand + water.

Solid – Solid

Alloys, baking powder.

Key idea
What Are Pure Substances
Everyday “pure”

Means nothing cheap or harmful has been added.

Scientific “pure”

Only one type of particle — cannot be separated further by any physical process.

Key idea
Electricity splits water into hydrogen and oxygen gas.
Proof water isn't one pure substance. An element is made of identical atoms that cannot be broken down any simpler — like gold, carbon, or oxygen.
Key idea
Metals, Non-metals, and Metalloids

Metals

Gold, silver, iron, aluminium.

Non-metals

Carbon, sulfur, hydrogen, oxygen.

Metalloids

Silicon, boron — properties in between.

Key idea
A compound's properties are completely different from its elements.
Water's hydrogen and oxygen are so tightly bound chemically that no physical method can separate them.
Key idea
Iron + Sulfur: Mixture vs Compound
Not heated · a mixture

Grey specks and yellow powder stay visible; a magnet still attracts the iron.

Heated · a compound

A uniform black mass forms — no longer attracted to a magnet at all.

Key idea
Minerals

Usually compounds

Quartz, calcite, and mica are compounds — most rocks are mixtures of minerals.

Occasionally elements

Native minerals like gold and silver are pure elements found in nature.

Chapter · key terms to remember
Key Terms

Mixture

Substances combined without a chemical reaction.

Alloy

A uniform mixture of two or more metals.

Pure substance

Only one type of particle; can't be separated physically.

Chapter · key terms to remember
More Key Terms

Element

Identical atoms; cannot be broken down further.

Atom / Molecule

An element's particle / atoms combined together.

Compound

Elements chemically combined in a fixed ratio.

Chapter · key terms to remember
More Key Terms

Mineral

A natural solid with fixed composition.

Opening

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