What everything is made of — elements, compounds and mixtures — and how particles behave as solids, liquids and gases.
Theme · StructureStructure 1.1SL & HL — same content
This sub-topic is examined identically at SL and HL — there is no additional Higher Level content in Structure 1.1. It sets up everything else in chemistry: matter is made of particles, and how those particles are arranged and how fast they move decides whether you have a solid, a liquid or a gas.
👆 Drag the temperature slider in the simulator · click the particle diagrams
1. Elements, compounds & mixtures S1.1.1
Everything is built from atoms. How those atoms are combined tells you what kind of substance you have. Click each box to see what the particle picture is showing.
Interactive · click each particle diagram
Click a boxEach shows how atoms are combined. One colour = one element; joined circles = chemically bonded.
ElementOne type of atom only; cannot be chemically broken down into simpler substances.
CompoundTwo or more elements chemically bonded in a fixed ratio; new properties, only separated chemically.
MixtureTwo or more substances not chemically bonded, in no fixed ratio; keep their own properties; separated physically.
Homogeneous mixtures have uniform composition throughout (e.g. salt water); heterogeneous mixtures have visibly different parts (e.g. sand and iron filings). Because mixtures aren't bonded, they're separated by physical methods — filtration, evaporation, distillation, recrystallisation and chromatography.
2. States of matter & the particle model S1.1.2
The kinetic molecular theory pictures matter as tiny particles in constant motion. Drag the temperature up and watch the particles gain energy, break free of their fixed positions, and finally spread out to fill the container.
Live particle simulator · drag the temperature
❄ coldhot 🔥
State
Solid
Arrangement
Regular, packed
Movement
Vibrate in place
Solid: particles are close together in a fixed, regular arrangement and can only vibrate. Heat gives them more kinetic energy.
Changes of state S1.1.2
3. Temperature & kinetic energy S1.1.3
Temperature in kelvin (K) is a measure of the average kinetic energy of particles. The kelvin and Celsius scales rise in equal-sized degrees, so you convert by adding or subtracting 273.15 (use 273 in most exam work). At absolute zero (0 K, −273.15 °C) particle motion is at a minimum. Type a value to convert:
⇌
25 °C = 298 KRoom temperature. Add 273.15 to go from °C to K; subtract to go back. Kelvin can never be negative — 0 K is absolute zero.
Common mistakes examiners see
Is a compound the same as a mixture?✗ Both are just several elements together, so they're the same.✓ A compound is chemically bonded in a fixed ratio with new properties; a mixture is not bonded, in no fixed ratio, and keeps each substance's properties.
When ice melts, what happens to the particles?✗ The particles themselves melt / get smaller.✓ The particles don't change — they gain kinetic energy, break out of the fixed lattice and can now move past each other.
How do you convert 20 °C to kelvin?✗ Multiply by some factor.✓ Add 273(.15): 20 °C = 293 K. The degrees are the same size on both scales.
Can temperature go below 0 K?✗ Yes, kelvin can be negative like Celsius.✓ No. 0 K (absolute zero) is the lowest possible temperature; kelvin values are never negative.