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1.7Chapter 1: The Particle Model and States of Matter

Models in science — Alhussan Chemistry - Stage 7 Revision Notes & Topical Questions

5 min read 7 parts Lesson 7 of 8 3 quizzes

📚 Alhussan Chemistry - Stage 7 Hub / Topical Revision
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Lesson summary

1.7 Models in science — Strengths and Limitations of the Particle Model — Alhussan International Academy — Chemistry (Stages 7–9) notes: Define a model in science and evaluate the strengths and limitations of the particle model.Model = an idea that explains observations and helps…

  • Scale model comparison
  • Representing the particle model
  • Other models
  • Not perfect copies
  • Shape of states
  • Compression

Part 1 of 5What a model is

What a model is
Model
Model an idea that explains observations and helps in making predictions.
  • It is a simplified way of describing something too small, too large, too slow or too complicated to observe directly.
Scale model comparison
  • Scale model comparison a model truck has the same colour and a similar shape as a real truck,
    • but it is smaller and cannot move by itself or carry heavy loads.
Representing the particle model
  • Representing the particle model it can be imagined, drawn, or shown with something else such as peas.
Other models
  • Other models some represent very small things such as particles and cells, and others very big things such as the Solar System.
  • A globe is a model of the Earth, a food web models feeding relationships and a circuit diagram models an electrical circuit.
Not perfect copies
  • Not perfect copies models are tested and improved as new evidence appears.

Part 2 of 5What the particle model explains well

What the particle model explains well
Shape of states
  • Shape of states solids have a fixed shape and volume, liquids take the shape of a container and gases fill it.
  • It explains why liquid water takes the shape of a cup and solid water (ice) does not.
Compression
  • Compression gases are easy to compress and solids are not.
Expansion
  • Expansion substances expand when heated because the particles move further apart.
Changes of state
  • Changes of state a solid melts, a liquid boils and a gas condenses when energy is added or removed.
Diffusion
  • Diffusion the spreading of particles from high concentration to low concentration.
  • Moving water particles collide with dye particles and spread them through the liquid.
  • The model predicts that diffusion is faster in a gas than a liquid and faster when warm, and experiments agree.
Predictions
  • Predictions if particles hold together strongly in solid gold, gold has a high melting point.
Confidence
  • Confidence when a prediction is confirmed by experiment, confidence in the model grows.

Part 3 of 5Limitations of the model

Limitations of the model
Every model is simpler than reality, which makes it useful, but it can never be perfect.
Particle shape
  • Particle shape in the model every particle is a solid sphere.
  • In reality different particles have different shapes, such as a water molecule, and particles are not solid.
  • Particles are mostly empty space, and atoms have an internal structure.
Movement
  • Movement diagrams show particles at rest, but in reality they are always moving.
Dimensions
  • Dimensions diagrams are two-dimensional but real substances are three-dimensional.
Forces
  • Forces particle diagrams usually do not show the forces between particles.
Spacing
  • Spacing the empty space is not shown to scale, because particles in a gas are much further apart than drawings can show.
Types of particle
  • Types of particle all particles are drawn the same, so atoms, ions and molecules are not distinguished.
Accuracy
  • Accuracy the model does not explain all observations perfectly, and predictions are sometimes not accurate.
Usefulness
  • Usefulness even with these limitations the particle model is still useful.

Part 4 of 5Comparing models

Comparing models
Other models such as a ball-and-stick model or a computer animation show other features.
No single model shows everything, so the best one depends on the question being asked.

Part 5 of 5Evaluating a model

Three questions
  • Three questions what does the model represent, what does it explain, and what does it leave out?
A good evaluation names what the model correctly explains, gives a specific feature it cannot show, and says why that matters.
  • The particle model explains why gases compress easily because the particles are far apart.
  • Drawing particles as identical hard spheres does not show that atoms have an internal structure, so it cannot explain how atoms bond or react.

Key terms

TermMeaning
ModelAn idea that explains observations and helps make predictions.
PredictionA statement of what will happen, based on a model or evidence.
LimitationA weakness or feature that a model does not show correctly.
DiffusionSpreading of particles from high to low concentration.
Particle modelA model of matter as tiny moving particles.
Solar SystemThe Sun and the objects that orbit it, a very large thing that is modelled.

Avoid these mistakes

1
Saying a model is a true picture of reality — it is a simplification.
2
Saying a limited model is useless — it can still be very helpful.
3
Thinking gas particles in a diagram are actually spaced the way they are drawn.
4
Forgetting that particles in diagrams are always moving.

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