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Chemistry · Chapter 1: Introduction to Chemistry
Matter and its Classification
Matter, the three states of matter and the particle model, and how matter is classified into pure substances and homogeneous and heterogeneous mixtures.
Key termRememberExampleWatch out
01Concept
Matter is anything that has mass and occupies space (has volume). Your desk, the water you drink and the air you breathe are all matter.
The three states of matter
All matter is made of tiny particles (atoms, molecules or ions). The way these particles are arranged and move decides whether a substance is a solid, a liquid or a gas.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes the shape of its container | Fills the whole container |
| Volume | Fixed | Fixed | Not fixed |
| Particles | Very close, in a regular pattern | Close, but no pattern | Far apart |
| Movement | Vibrate in place | Slide past each other | Move fast in all directions |
| Can it be compressed? | No | Hardly | Yes, easily |
| Example | Ice, iron, salt | Water, milk, petrol | Air, steam, LPG |
Classifying matter
Chemists sort matter into two big groups: pure substances and mixtures.
- A pure substance has a fixed composition and the same properties throughout. It is either an element or a compound. Pure water always boils at 100 °C at sea level.
- A mixture contains two or more substances that are not chemically joined, and its composition can vary. Tea can be made with more or less sugar.
| Mixture type | Meaning | Examples |
|---|---|---|
| Homogeneous | Same composition throughout; you cannot see the separate parts | Air, salt water, brass |
| Heterogeneous | Composition not the same throughout; you can often see the parts | Sand and water, soil, oil in water |
02Real World Examples
LPG cylinders
Gas is easy to compress, so a large amount of LPG is squeezed into a cylinder as a liquid under pressure.
Doodh-patti
Tea with milk and sugar is a mixture: you can make it stronger or sweeter, so its composition varies.
Muddy water after rain
Mud in water is a heterogeneous mixture. Leave it for a while and the mud settles at the bottom.
Brass utensils
Brass is a homogeneous mixture (an alloy) of copper and zinc.
03Practice Questions
Try to answer in your own words first, then open the model answer.
Short questions
Q1.Define matter. Is light matter?Show answer
Answer
Matter is anything that has mass and occupies space. Light is not matter: it has no mass and takes up no space; it is a form of energy.
Q2.Why can gases be compressed but solids cannot?Show answer
Answer
In a gas the particles are far apart, so there is a lot of empty space to squeeze them into. In a solid the particles are already packed closely, so there is no space.
Q3.Differentiate between a pure substance and a mixture.Show answer
Answer
| Pure substance | Mixture |
|---|---|
| Fixed composition | Composition can vary |
| Elements or compounds | Two or more substances not chemically joined |
| Fixed melting and boiling points | Melts or boils over a range of temperatures |
| Pure water, iron | Air, tea, soil |
Q4.What are homogeneous and heterogeneous mixtures? Give two examples of each.Show answer
Answer
- Homogeneous: same composition throughout. Air, salt water.
- Heterogeneous: composition not the same throughout. Sand in water, soil.
Long questions
Q5.Compare solids, liquids and gases using the particle model.Show answer
Answer
| Solid | Liquid | Gas | |
|---|---|---|---|
| Arrangement | Close, regular pattern | Close, irregular | Far apart, random |
| Movement | Vibrate in place | Slide past each other | Move fast in all directions |
| Shape | Fixed | Takes container's shape | Fills container |
| Volume | Fixed | Fixed | Not fixed |
| Compression | No | Hardly | Easily |