Particulate Theory of Matter

Use evidence from diffusion and related observations to explain why matter is considered particulate. CXC profiles: Knowledge & Comprehension, Use of Knowledge, Experimental Skills.

ChemistryLesson 1 of 2CXC-aligned practiceKC • UK • Experimental Skills

CHEM

CSEC Chemistry • Lesson 1 of 2Particulate Theory · Myers Science Hub Student Centre

CSEC Centre MSH Home

CourseCSEC Chemistry

Practice formatMCQ • Structured • Experimental

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Objectives Notes Video MCQ Structured Experiment

Learning objectives

State the key ideas of the particulate theory of matter.
Explain diffusion using particle motion and concentration.
Use observations as evidence for particles that are too small to see directly.
Design a simple investigation that tests how temperature affects diffusion.

CXC link: Specific Objective A1.1 requires students to explain how evidence supports the particulate theory of matter. The syllabus explicitly points to diffusion and practical work.

Core notes

1. Matter is made of particles

All matter is composed of extremely small particles. In solids they are closely packed in fixed positions; in liquids they remain close but can move past one another; in gases they are far apart and move rapidly and randomly.

2. Particles are always moving

Particles possess kinetic energy. Increasing temperature generally increases their average kinetic energy, so particle motion becomes faster.

3. Diffusion

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration because of random particle motion. It continues until the particles are more evenly distributed.

4. Evidence

The spreading of perfume through a room, potassium manganate(VII) through water, or ammonia and hydrogen chloride gases through a tube provides indirect evidence that tiny particles move and mix.

How to write the explanation CXC wants

A strong answer links observation → particle idea → conclusion. Example structure: “The coloured particles spread from the concentrated region throughout the water without stirring. This shows that particles are in constant random motion; therefore matter is made of moving particles.”

Video lesson

Verified CSEC-focused video: CSEC Chemistry – Exploring States of Matter.

Paper 02-style structured questions

4. Define diffusion.KC • 2 marks

Award 1 mark for movement from higher to lower concentration and 1 mark for movement caused by random particle motion / until more evenly distributed.

5. A crystal of potassium manganate(VII) is placed at the bottom of a beaker of still water. After 30 minutes the purple colour is seen throughout the water. Explain this observation in terms of particles.UK • 3 marks

Particles from the crystal enter the water (1); they move randomly from the high-concentration region near the crystal toward regions of lower concentration (1); over time they become distributed throughout the water / diffusion occurs (1).

Experimental Skills question

6. Plan an investigation to determine the effect of water temperature on the rate at which a soluble coloured substance diffuses.XS/PD • 8 marks

Your plan should include a hypothesis, manipulated variable, responding variable, two controlled variables, a clear method, and how the results would be used to reach a conclusion.

Indicative marking points: testable hypothesis such as “as temperature increases, diffusion rate increases” (1); manipulate water temperature (1); measure time for colour to reach a stated endpoint or calculate distance/time (1); control volume of water and amount/size/concentration of coloured substance (2); use equal containers, establish several temperatures, add substance in same way, time without stirring, repeat trials (2); compare mean time/rate against temperature and state conclusion from trend (1).

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