Learning outcomes

Kinetic Model of MatterKinetic Model of Matter

T H E M E T H R E E : T H E R M A L P H Y S I C S

C h a p t e r 8Learning outcomes• Compare the properties of solids, liquids and

gases• Describe quantitatively the molecular

structure of solids, liquids and gases, relating their properties to the forces and distances between molecules and to motion of molecules

• Describe the relationship between motion of molecules and temperature



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Three states of matter Solid Liquid Gas

• For example, iceberg, sea water and steam

8.1 States of Matter



C h a p t e r 88.1 States of MatterProperties of Solids, Liquids and Gases

Solid Liquid Gas

• Fixed shape• Fixed volume

• Fixed volume• Does not have fixed shape• Assumes shape of container

• No fixed shape• No fixed volume• Assumes the shape and volume of container

• Not compressible

• Not easily compressible

• Highly compressible

• Does not flow easily

• Flows easily • Flows easily



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Molecular Structure of Solids, Liquids and Gases

SolidsDistances between molecules• Molecules arranged close together in regular

pattern• Incompressible because molecules are close

together with little space between them




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SolidsForces between molecules • Balanced forces between molecules hold them in

fixed positions• Molecules vibrate about fixed positions,

alternately attracting and repelling one another• Strong attractive forces prevent molecules from

leaving fixed positions while repulsive forces between atoms prevent them from collapsing into one another.

• Attractive and repulsive forces explains why a solid has fixed shape and fixed volume.

8.1 States of MatterMolecular Structure of Solids, Liquids and Gases



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SolidsMotion of the molecules• When a solid is heated, molecules gain energy

and vibrate more.• Separation between molecules increase slightly

and the solid expands.





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LiquidDistances between molecules• Molecules not arranged in regular pattern • Molecules slightly further apart than in solids• Liquids cannot be easily compressed as

molecules are close together with little space between them.





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Liquid• Forces between molecules and motion of

the molecules• Molecules vibrate to and fro, alternately

attracting and repelling one another.• Molecules not held in fixed position by attractive

forces.• Molecules move among one another throughout

the liquid. • Explains why liquids flow and take the shape of

container





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Liquid• Forces between molecules and motion of

the molecules• Attractive forces between molecules make it

difficult for molecules to leave the liquid. • Thus liquids have fixed volume.• When a liquid is heated, molecules vibrate and

move about more vigorously.• Thus liquid expands, but only very slightly.





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GasDistances between molecules• Molecules are far apart• Mainly empty space between molecules• That is why gas can be compressed easily.





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Forces between molecules & motion of molecules

• Molecules move randomly at high speed• Intermolecular repulsive forces act only

when molecules collide with one another and with the walls of container.

• Molecules are so far apart that intermolecular attractive forces are negligible in a gas.

• A gas is thus able to expand and fill a container completely.




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The three states of matter are solid, liquid and gas.



C h a p t e r 88.2 Kinetic Model

• The kinetic theory of matter states that all matter is made up of a large number of tiny atoms or molecules which are in continuous motion.

• Molecules are too small to be seen directly.• Existence of particles in continuous motion

has been demonstrated by Brownian motion and diffusion.



C h a p t e r 88.2 Kinetic ModelMotion of Molecules and Temperature• When temperature increases, thermal

energy of the molecules increases and the molecules move faster.

• The molecules gain kinetic energy.



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1. When the temperature increases, kinetic energy of the molecules also increases.



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Learning outcomes