Big idea
Matter exists in different states because of how its particles are arranged and how much energy they have. Every substance also has its own physical properties.
01States of matter and the particle model
The particle model helps explain the three common states of matter.
- Solid — particles tightly packed, vibrate in place, fixed shape and volume
- Liquid — particles close but can slide past each other, fixed volume, takes shape of container
- Gas — particles far apart and move freely, no fixed shape or volume
02Changes of state
Adding heat energy makes particles vibrate or move faster; removing heat energy slows them down. This causes changes between states, always at a fixed temperature for a given substance (its melting or boiling point).
- Melting — solid → liquid
- Freezing — liquid → solid
- Evaporation / boiling — liquid → gas
- Condensation — gas → liquid
- Sublimation — solid → gas directly (e.g. dry ice)
03Physical properties
A physical property can be observed or measured without changing the substance into something new.
Examples include colour, hardness, melting point, boiling point, density, and whether something conducts electricity or heat.
04Density
Density tells us how much mass is packed into a given volume. Denser objects sink in less dense fluids.
density = mass ÷ volume (g/cm³ or kg/m³)
Example. A rock has mass 150 g and volume 50 cm³. Density = 150 ÷ 50 = 3 g/cm³.
| Term | 한국어 | Meaning |
|---|---|---|
| particle model | 입자모형 | A model that explains matter as tiny moving particles |
| melting point | 녹는점 | Temperature at which a solid turns to liquid |
| boiling point | 끓는점 | Temperature at which a liquid turns to gas |
| density | 밀도 | Mass per unit volume of a substance |
| sublimation | 승화 | Solid changing directly into gas |
| physical property | 물리적 성질 | A property observable without creating a new substance |
Quick check — tap a question to reveal the answer
Put these in order of how closely packed their particles are: gas, solid, liquid.
Solid (most packed) → liquid → gas (most spread out).
What is the name for a solid turning directly into a gas?
Sublimation.
A block has mass 200 g and volume 100 cm³. What is its density, and would it float on water (density 1 g/cm³)?
Density = 200 ÷ 100 = 2 g/cm³. It would sink, because it is denser than water.