Describe the arrangement and movement of particles in a solid.

Touching in a regular pattern; they only vibrate about fixed positions.

Describe the particles in a liquid.

Close together in an irregular arrangement; they slide past each other.

Describe the particles in a gas.

Far apart, moving quickly and randomly, with very weak forces between them.

Why can a gas be compressed?

There are large spaces between the particles.

Solid changing directly to gas without becoming a liquid.

How does evaporation differ from boiling?

Evaporation is at the surface at any temperature below the boiling point; boiling is throughout the liquid at the boiling point.

Why does evaporation cool a liquid?

The fastest particles escape, so the average kinetic energy of the remaining particles falls.

Name four things that increase the rate of evaporation.

Higher temperature, larger surface area, wind (moving air) and drier air.

Why is the temperature constant on a flat part of a heating curve?

The energy supplied is used to overcome forces between particles, not to increase their kinetic energy.

What does a pure substance do when it melts?

It melts at one sharp, fixed temperature.

What does an impure substance do when it melts?

It melts over a range of temperatures and below the pure melting point.

Give two limitations of the particle model.

Particles are drawn as solid spheres, and the forces between them are not shown.

States of matter and particle modelIB MYP Sciences: Flashcards

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What are the properties of a solid?

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What are the properties of a solid?: Fixed shape, fixed volume, cannot be compressed.
Describe the arrangement and movement of particles in a solid.: Touching in a regular pattern; they only vibrate about fixed positions.
Describe the particles in a liquid.: Close together in an irregular arrangement; they slide past each other.
Describe the particles in a gas.: Far apart, moving quickly and randomly, with very weak forces between them.
Why can a gas be compressed?: There are large spaces between the particles.
What is sublimation?: Solid changing directly to gas without becoming a liquid.
How does evaporation differ from boiling?: Evaporation is at the surface at any temperature below the boiling point; boiling is throughout the liquid at the boiling point.
Why does evaporation cool a liquid?: The fastest particles escape, so the average kinetic energy of the remaining particles falls.
Name four things that increase the rate of evaporation.: Higher temperature, larger surface area, wind (moving air) and drier air.
Why is the temperature constant on a flat part of a heating curve?: The energy supplied is used to overcome forces between particles, not to increase their kinetic energy.
What does a pure substance do when it melts?: It melts at one sharp, fixed temperature.
What does an impure substance do when it melts?: It melts over a range of temperatures and below the pure melting point.
Give two limitations of the particle model.: Particles are drawn as solid spheres, and the forces between them are not shown.

Exam questions on States of matter and particle model

At a school science fair in Dubai, a student shows a block of dry ice (solid carbon dioxide) in a bowl. The block gets smaller and a cold gas pours over the edge of the bowl, but no liquid collects in the bowl. The student explains the demonstration using the particle model, in which each particle is drawn as a small solid sphere.
Explain, using the particle model, why a gas can be compressed into a smaller volume but a solid cannot.2 marks
In Dubai in summer, wet laundry hung on a balcony dries within a couple of hours, even though the temperature is far below 100 °C and the water never boils. A student wants to explain why the water leaves the clothes and why the air near the laundry feels slightly cooler.
Explain, in terms of particles, why evaporation makes the remaining liquid cooler.2 marks
A student heats a solid sample of pure stearic acid in a water bath and records its temperature every minute. The temperature rises steadily from 20 °C, stays at 69 °C for several minutes while the solid melts, and then rises again.
State the melting point of stearic acid and explain, in terms of particles and energy, why the temperature stays constant while it melts.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).