Chapter 4Chapter 4

States of MatterStates of Matter

Section 4-1Section 4-1

SolidsSolids

Quiz next class on Sec. Quiz next class on Sec. 4-14-1

Everyday,

water changes from a

solid to a liquid to a

gas and

back again

How can we explain this?

Let’s do a quick review of what you Let’s do a quick review of what you already know:already know:

Matter has three states:Matter has three states:

1.1. SolidSolid

2.2. LiquidLiquid

3.3. GasGas

Matter is anything that takes up Matter is anything that takes up space and has mass.space and has mass.

More reviewMore review

Most matter is made up atoms and Most matter is made up atoms and molecules.molecules.

An atom is the smallest particle that makes An atom is the smallest particle that makes up a given element of matter.up a given element of matter.

When two or more atoms combine, they make a particle called a molecule.

Examples of moleculesExamples of molecules

H

OH

Water

C

C

C

C

C

C

O

O

O

O

O

O

H

H

H

H

H

H

H

H

H

H

H

H

Glucose

Blood sugar

N N

Nitrogen

SolidLiquid

Gas

??????

Why is water a liquid, nitrogen a gas Why is water a liquid, nitrogen a gas and glucose a solid?and glucose a solid?

What makes a solid a solid?What makes a solid a solid? a liquid a liquid?a liquid a liquid? a gas a gas?a gas a gas?

One clue to this mystery was first One clue to this mystery was first reported in 1827 by scientist reported in 1827 by scientist Robert Brown –Robert Brown –– Brownian MotionBrownian Motion

Under a microscope, dust particles can be seen to movein a random, jerky way.

The water molecules surrounding The water molecules surrounding the dust particle are in constant, the dust particle are in constant, random motion.random motion.

When they hit the dust particle, When they hit the dust particle, they push it in random directionsthey push it in random directions

Matter in motionMatter in motion

The idea that the particles (atoms The idea that the particles (atoms and molecules) of all matter are and molecules) of all matter are in constant, random motion is in constant, random motion is called the called the kinetic theory of kinetic theory of mattermatter..

Kinetic Theory of MatterKinetic Theory of Matter

All matter is made of atoms and All matter is made of atoms and molecules.molecules.

These particles are always in motion.These particles are always in motion.

The higher the temperature, the The higher the temperature, the faster the particles move.faster the particles move.

At the same temperature, heavier At the same temperature, heavier particles move slower and lighter particles move slower and lighter particles move faster.particles move faster.

Temperature and HeatTemperature and Heat

What makes hot tea different What makes hot tea different from cold iced tea?from cold iced tea?

– Same particlesSame particles

– movement of particles is differentmovement of particles is different

Higher temp = faster moving Higher temp = faster moving particlesparticles

Lower the temperature and the Lower the temperature and the particles slow down.particles slow down.

At very low temperatures the At very low temperatures the motion of the molecules is very motion of the molecules is very slow.slow.

You cannot make things so cold You cannot make things so cold that the motion completely stops, that the motion completely stops,

Temperature and HeatTemperature and Heat

but . . .

scientists have come close.scientists have come close.

absolute zero.

The temperature at which the The temperature at which the particles of matter would particles of matter would completely stop is calledcompletely stop is called

Absolute zero is

- 273.15° C

You can’t get colder than that,no matter how hard you try

Transfer of heatTransfer of heat

When hot matter touches colder When hot matter touches colder matter, faster moving particles matter, faster moving particles collide with slower moving particles.collide with slower moving particles.

The faster moving particles give The faster moving particles give some of their energy to the slower some of their energy to the slower moving particles.moving particles.

Matter in the solid Matter in the solid statestate In a solid, the particles vibrate or In a solid, the particles vibrate or

shake back and forthshake back and forth but do not move from their but do not move from their

position in respect to each other.position in respect to each other.

The particles vibrate about a fixed position.

Crystals orCrystals or Crystalline Solids Crystalline Solids Particles of crystals are arranged Particles of crystals are arranged

in repeating geometric patternsin repeating geometric patterns

Table salt crystals are shaped like Table salt crystals are shaped like cubes.cubes.

Diamond, a form of carbon, is Diamond, a form of carbon, is also a crystalline solid.also a crystalline solid.– the crystals are shaped something the crystals are shaped something

like pyramids.like pyramids.

Non-crystalline solidsNon-crystalline solids

Many solids do not form crystals.Many solids do not form crystals. Their molecules do not arrange Their molecules do not arrange

into repeating patternsinto repeating patterns– often because they are too large.often because they are too large.

Examples:Examples:– glassglass– many plasticsmany plastics

How does a solid How does a solid become a liquid?become a liquid?

1.1. Start with very cold ice and Start with very cold ice and gradually heat it.gradually heat it.

If you could see the molecules, If you could see the molecules, you would see each molecule you would see each molecule shaking faster and faster, shaking faster and faster,

but still held in one but still held in one position by the other position by the other molecules around it.molecules around it.

Keep heating your iceKeep heating your ice

When the temperature reaches 0° When the temperature reaches 0° C, the molecules begin to break free.C, the molecules begin to break free.

The molecules begin to move freely The molecules begin to move freely around each other.around each other.

The molecules enter the liquid state.The molecules enter the liquid state.

Melting point = Melting point =

the temperature at which a the temperature at which a substance changes from a solid to substance changes from a solid to a liquid.a liquid.

Heat (kilojoules)

Tem

pera

ture

(

C°)

0°

0-20°

20°

60°

Heat (kilojoules)

Tem

pera

ture

(

C°)

0°

0-20°

20°

60°

The amount of heat required to The amount of heat required to melt 1 kg of a solid is called its melt 1 kg of a solid is called its

heat of fusion

measured in

kilojoules per kilogram

k J / k g

Heat (kilojoules)

Tem

pera

ture

(

C°)

0°

heat of fusion

Water’s heat of fusion isWater’s heat of fusion is 334 kJ/kg334 kJ/kg

That is the same amount of energy That is the same amount of energy you would spend if you climbed all you would spend if you climbed all the stairs in a 110-story tall building.the stairs in a 110-story tall building.

No, not a 110-foot tall building . . .

a 110-story building!

FreezingFreezing

As you know, if you can melt As you know, if you can melt something, you can cool the liquid something, you can cool the liquid again to freeze it.again to freeze it.

When you cool a liquid, the When you cool a liquid, the particles begin to slow down.particles begin to slow down.

The attractive forces between the The attractive forces between the particles begin to catch the particles begin to catch the particles,particles,

and crystals begin to form.and crystals begin to form.

Freezing point =Freezing point =– the temperature at which attractive the temperature at which attractive

forces trap particles in a cooling forces trap particles in a cooling liquid and form crystals.liquid and form crystals.

Think: If the melting point of iron is 1,535° C, at what temperature does iron freeze?

Non-crystalline solidsNon-crystalline solids

Non-crystalline solids, like glass, Non-crystalline solids, like glass, butter or wax, do not have a butter or wax, do not have a definite freezing or melting point.definite freezing or melting point.

• If you slowly heat cold butter, it gradually gets softer and softer until it is completely liquid.