The Particulate Nature of Matter

Syllabus objectives :(a) Describe the solid, liquid and

gaseous states of matter and explain their interconversion in terms of the kinetic particle theorykinetic particle theory and of the energy changes involved.

(b) Describe and explain evidenceevidence for the movement of particles in liquid and gases.

Matter - a Particle Explanation

Matter is anything that occupies space and has mass.

Matter is made up of small particles - DemocritusDemocritus

By convention there is color,by convention sweetness, by convention bitterness,

but in reality there are atomsatoms and space. -Democritus 460-371 BC

The Kinetic Particle Theory The The Kinetic Particle theoryKinetic Particle theory of matter of matter states thatstates that all matter is made up of all matter is made up of tiny tiny

particlesparticles;; all particles are in all particles are in constant constant

random motionrandom motion

Particulate Nature of Matter - Evidence

From Diffusion experiments…

When a few drops of bromine are placed into a gas jar of air, the red-brown bromine

vapour spreads slowly upwards until the whole jar is

filled with a uniform brown vapour.


From Diffusion experiments………observations can be observations can be explained if we accept explained if we accept the idea that the the idea that the substances are made up substances are made up of small particles in of small particles in constant motion.constant motion.


From Diffusion experiments…..and during diffusion, ..and during diffusion, the bromine particles the bromine particles move into the spaces move into the spaces between the air particles between the air particles while the air particles while the air particles move into the spaces move into the spaces between the bromine between the bromine particles..particles..


From changes in volume - mixing water & alcohol

……observation can be explained observation can be explained if we agree that water and if we agree that water and ethanol are made of particles. ethanol are made of particles.

There are There are empty empty spacesspaces between the ethanol particles. between the ethanol particles. The water particles move into The water particles move into these spaces.these spaces.50 cm3 of water mixed with

50 cm3 of alcohol gives98 cm3 of mixture


From changes in volume - mixing water & alcohol ……observation can be explained observation can be explained

if we agree that water and if we agree that water and ethanol are made of particles. ethanol are made of particles.

There are There are spacesspaces between the between the ethanol particles. The water ethanol particles. The water particles move into these particles move into these spaces.spaces.

By convention there is color,By convention there is color,by convention sweetness, by convention sweetness, by convention bitterness, by convention bitterness,

but in reality but in reality there are there are atomsatoms and and spacespace. .

--DemocritusDemocritus 460-371 BC 460-371 BC

By convention there is color,By convention there is color,by convention sweetness, by convention sweetness, by convention bitterness, by convention bitterness,

but in reality but in reality there are there are atomsatoms and and spacespace. .

--DemocritusDemocritus 460-371 BC 460-371 BC


From changes of state


Others - dissolving, fusing of metals

The Particles of Matter

Atoms Molecules Ions

The 3 States of Matter

Property solid liquid gas

Definite massDefinite mass

Definite shapeDefinite shape

Definite volumeDefinite volume

The Kinetic Particle Theory

The The Kinetic Particle theoryKinetic Particle theory of matter of matter states thatstates that all matter is made up of tiny all matter is made up of tiny

particles;particles; all particles are in constant all particles are in constant

random motionrandom motion



Property solid liquid gas

Packing of particlesPacking of particles closely packed closely packed far apartfar apart

Arrangement ofArrangement ofparticlesparticles

Orderly Not orderly Not orderlyOrderly Not orderly Not orderlyvibrate and vibrate and rotate rotate about about fixed fixed positions positions

vibrate andvibrate andslide over oneslide over oneanotheranother

move rapidly move rapidly and atand atrandom in anyrandom in anydirectiondirection

Attractive forcesbetween particles very strong less strong almost no

Movement ofMovement ofparticlesparticles

The Solid State

Property

•Definite shapeDefinite shape•Definite volumeDefinite volume

particles cannot move particles cannot move freely; can only vibrate freely; can only vibrate about fixed positionsabout fixed positions

• Cannot be Cannot be compresssecompresssed d

Particles are packed Particles are packed very closely very closely togethertogether

Explanation

The Liquid State

Property

• No definite No definite shapeshape

particles can slide over particles can slide over one anotherone another

• Cannot be Cannot be compresssedcompresssed; has fixed ; has fixed volumevolume

Particles are packed Particles are packed close togetherclose together

Explanation

The Gaseous State

Property

• No definite No definite shape or shape or volumevolume

particles can move about particles can move about rapidly and randomly in rapidly and randomly in any direction as forces any direction as forces between particles are between particles are weakweak• Can be Can be

compresssedcompresssedParticles are far Particles are far apart, with a lot of apart, with a lot of empty space empty space between thembetween them

Explanation

Changes of State

GASGAS

SOLIDSOLID LIQUIDLIQUIDmelting

boiling

subl

imat

ion

freezing

condensation

cond

ensa

tion

Melting - in terms of Kinetic Particle Theory

• When a solid is heated, When a solid is heated, heat energy is absorbedheat energy is absorbed. . This causes the particles to This causes the particles to gain kinetic energygain kinetic energy and to and to vibrate faster. vibrate faster.

• At a certain temperature At a certain temperature ((melting pointmelting point, , the the vibrations become so violent that the particles are vibrations become so violent that the particles are able to able to overcome some of the attractive forces overcome some of the attractive forces between them and break away from each otherbetween them and break away from each other. .

The solid then becomes a liquid.The solid then becomes a liquid. Melting occurs.Melting occurs.

Freezing - in terms of Kinetic Particle Theory

• When a liquid is cooled, When a liquid is cooled, heat energy is releasedheat energy is released. . This causes the particles to This causes the particles to lose kinetic energylose kinetic energy and to and to vibrate slowervibrate slower. .

• At a certain temperature At a certain temperature ((freezing pointfreezing point, the , the vibrations become so slow that the particles are vibrations become so slow that the particles are unable to overcome the attractive forces between unable to overcome the attractive forces between them and are drawn towards each other in orderly them and are drawn towards each other in orderly and fixed positions. and fixed positions. The liquid then becomes a solidThe liquid then becomes a solid. . Freezing occursFreezing occurs..

Boiling - in terms of Kinetic Particle Theory

• When a liquid is heated, When a liquid is heated, heat energy is heat energy is absorbedabsorbed. . This causes the particles to This causes the particles to gain gain kinetic energykinetic energy and and move fastermove faster. .

• At a certain temperature At a certain temperature boiling pointboiling point), the ), the vibrations become so violent that the vibrations become so violent that the particles particles throughout the liquid are able to break away throughout the liquid are able to break away from the forces holding them togetherfrom the forces holding them together. . The liquid then becomes a gas. The liquid then becomes a gas. Boiling occursBoiling occurs..

Sublimation - in terms of Kinetic Particle Theory

• When the solid is heated, When the solid is heated, heat energy is heat energy is absorbedabsorbed. . Particles Particles gain gain kinetic energykinetic energy and and move move fasterfaster. .

• At a certain temperature At a certain temperature the vibrations become so the vibrations become so violent that the violent that the particles particles break free completely break free completely from each otherfrom each other, and , and move randomly.move randomly.The solid then becomes a The solid then becomes a gas directly. gas directly. Sublimation Sublimation occursoccurs..

Heating Curve

temperature (ºC)melting starts

temperature remains constant. Why?

melting completes

time from start (min)

melting point

SOLID

SOLID + LIQUIDLIQUID

Heat energy absorbed by the particles is used to overcome the forces of attraction holding the particles together in their fixed positions.

Cooling Curve

temperature remains constant.

Why?

freezing completes

freezing starts

freezing point (=melting point)

for pure substances

SOLID

LIQUID + SOLID

LIQUID

temperature (ºC)

time from start (min)

Heat loss due to cooling is exactly balanced by the heat energy liberated as the particles attract one another to form a solid.

Evaporation vs Boiling

BoilingBoiling EvaporationEvaporation

Takes place at boiling point of the

liquid

Takes place at any temperature below

takes place throughout the liquid

takes place at the surface of the liquid

very fast process very slow process

Similarity : Both involve the change of state from liquid to gas.

Differences :

GAS

Predicting physical states

Substance X has m.p. -460C and b.p. 1670C.What is its physical state at (i) room temperature (ii) -100C (iii) -500C ?

- 460C

s l

1670C

l g

SOLID LIQUID

250C

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The Particulate Nature of Matter