Nature of Matter: Elements, Compounds, and Mixtures
Look around: the staircase, the air, your water bottle, your clothes. Almost nothing you see is made of just one substance. How do substances combine — and how is combining different from just mixing?
Key idea
What Are Mixtures?
When substances are mixed and each keeps its own properties, the result is a mixture — its parts are called components.
Non-uniform mixture
Components are visible, even with a magnifying glass — like a sprout salad.
Uniform mixture
Components can't be told apart even under a microscope — like sugar dissolved in water. Alloys (like stainless steel, brass, bronze) are uniform metal mixtures.
Key idea
Is Air a Mixture?
1
Air is a uniform mixture
mostly nitrogen (~78%) and oxygen, plus argon, carbon dioxide, and water vapour.
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2
Proving CO2 is there
Lime water turns milky when exposed to air, because carbon dioxide reacts with it to form insoluble calcium carbonate.
Key idea
Types of Mixtures
Combination | Example
Gas – Gas
Air
Gas – Liquid
Soda water
Solid – Gas
Dust in air
Key idea
Types of Mixtures — continued
1
Liquid – Liquid
Vinegar, oil + water
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2
Solid – Liquid
Seawater, sand + water
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3
Solid – Solid
Alloys, baking powder
Key idea
What Are Pure Substances?
1
Everyday "pure"
Means nothing cheap or harmful has been added.
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2
Scientific "pure"
Contains no other substance at all — only one type of particle, and cannot be separated further by any physical process.
Key idea
Elements
Passing electricity through acidified water splits it into hydrogen and oxygen gas — proof water isn't a single pure substance.
Element
A pure substance made of identical particles (atoms) that cannot be broken down into anything simpler — like gold, carbon, or oxygen.
Key idea
Metals, Non-metals, and Metalloids
1
Metals
Gold, silver, iron, aluminium.
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2
Non-metals
Carbon, sulfur, hydrogen, oxygen.
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3
Metalloids
Silicon, boron — properties in between.
Key idea
Compounds
Water's hydrogen and oxygen are so tightly bound that no physical method can separate them — that's what makes water a compound.
Compound
Forms when elements combine chemically in a fixed ratio — with completely different properties from the elements themselves.
Key idea
Iron + Sulfur: Mixture vs Compound
| Iron + sulfur (not heated) | Iron sulfide (heated)
AppearanceGrey specks + yellow powder, visible — Uniform black mass
Magnet testIron is attracted — Not attracted at all
With dilute HClHydrogen gas (a "pop") — Hydrogen sulfide (rotten-egg smell)
Key idea
Classifying Matter
1
Elements
Pure substances, one kind of atom. Cannot be broken down further.
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2
Compounds
Pure substances, two or more elements combined chemically.
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3
Mixtures
Two or more substances combined, no chemical reaction, separable.
Key idea
Minerals
Usually compounds, occasionally elements. Most rocks are mixtures of minerals. Native minerals like gold and silver are pure elements found in nature; most others — quartz, calcite, mica — are compounds.
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.
Questions for your notebook
Write these down, then discuss
1
Assertion: Air is a mixture. Reason: A mixture forms when substances are mixed without any chemical change. Are both true, and does the reason explain the assertion?
2
Water (a compound) has very different properties from the oxygen and hydrogen it's made from. Justify this.
3
Which set is correctly matched? (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.
Project as-is — students copy the questions, then the class discusses answers together.