CHEMISTRY · Stage 7 · Chapter 1: The Particle Model and States of Matter
Chemistry 1.7 Models in science — Strengths and Limitations of the Particle Model
5 min read 5 parts Lesson 7 of 8
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
Section 1 of 5What a model is
- 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
- 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
- it can be imagined, drawn, or shown with something else such as peas.
- 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
- models are tested and improved as new evidence appears.
Section 2 of 5What the particle model explains well
- 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
- gases are easy to compress and solids are not.
- Expansion
- substances expand when heated because the particles move further apart.
- Changes of state
- a solid melts, a liquid boils and a gas condenses when energy is added or removed.
- 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
- if particles hold together strongly in solid gold, gold has a high melting point.
- Confidence
- when a prediction is confirmed by experiment, confidence in the model grows.
Section 3 of 5Limitations of the model
- Every model is simpler than reality, which makes it useful, but it can never be perfect.
- 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
- diagrams show particles at rest, but in reality they are always moving.
- Dimensions
- diagrams are two-dimensional but real substances are three-dimensional.
- Forces
- particle diagrams usually do not show the forces between particles.
- 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
- all particles are drawn the same, so atoms, ions and molecules are not distinguished.
- Accuracy
- the model does not explain all observations perfectly, and predictions are sometimes not accurate.
- Usefulness
- even with these limitations the particle model is still useful.
Section 4 of 5Comparing 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.
Section 5 of 5Evaluating a model
- 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.
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