5.2.1Solids, Liquids and Gases
Solids, Liquids and Gases — Edexcel International GCSE Science Double Award 4SD0 - Physics Revision Notes & Topical Questions
5 min read 4 parts Lesson 8 of 23
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Properties Compared
The shape, volume and compressibility of a substance follow from how its particles are arranged.
Solids
- Solids Solids have a fixed shape and fixed volume because strong forces hold their particles in place.
Liquids
- Liquids Liquids have a fixed volume but no fixed shape, since their particles can flow past one another.
Gases
- Gases Gases have no fixed shape or volume, so the gas spreads out to fill any container it is placed in.
Density trend
- Density trend Solids and liquids are much denser than gases because their particles are much closer together.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes the shape of its container | Fills its container |
| Volume | Fixed | Fixed | Fills its container |
| Compressibility | Very low | Very low | High |
Part 2 of 4Particle Arrangement and Motion
Particles are always in motion, but the type of motion depends on the state.
Particle Arrangement and Motion
Solid lattice
- Solid lattice Particles form a regular arrangement and vibrate about fixed positions.
Liquid spacing
- Liquid spacing Particles are close together in a disordered arrangement and move continuously around each other.
Gas spacing
- Gas spacing Particles are widely spaced and move rapidly in straight lines until they collide.
Attractive forces
- Attractive forces Forces between particles are strongest in solids, weaker in liquids and very small in gases.
Part 3 of 4Diffusion
Diffusion shows that particles in all three states are in constant motion.
1
Diffusion is the random movement of particles from a region of higher concentration to a region of lower concentration.
2
Gases diffuse quickly because their particles move fast and are widely separated from one another.
3
Liquids diffuse more slowly, as shown when a drop of dye spreads through still water over several minutes.
4
Solids diffuse extremely slowly, so mixing between the particles of two solids takes a very long time.
Part 4 of 4Exam Checklist & Tips
5.2.1 – Key Points for the Exam
- Particle model A way of describing matter as tiny particles whose arrangement and motion depend on the state.
- Diffusion The spreading of particles from high to low concentration by random motion.
- Lattice A regular, repeating arrangement of particles in a solid.
- Compressible A substance whose volume can be reduced by applying pressure.
- Intermolecular force An attractive force between neighbouring particles, weaker than chemical bonds.
Common Mistakes
- Saying solid particles do not move; they vibrate about fixed positions.
- Describing gas particles as touching each other inside a container.
- Describing particles as expanding when a gas is heated; the particles keep their size and only move faster.
- Confusing the forces between particles with the bonds inside a particle.
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