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Chapter 4 States of Matter

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# Chapter 4 States of Matter - PowerPoint PPT Presentation

Chapter 4 States of Matter. Section 4-1 Solids. Quiz next class on Sec. 4-1. 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 already know:. Matter has three states: Solid Liquid Gas

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### Chapter 4States of Matter

Section 4-1

Solids

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 already know:
• Matter has three states:
• Solid
• Liquid
• Gas

Matter is anything that takes up space and has mass.

More review
• Most matter is made up atoms and molecules.
• An atom is the smallest particle that makes up a given element of matter.
• When two or more atoms combine, they make a particle called a molecule.

O

H

C

O

H

H

H

C

H

Liquid

Glucose

Blood sugar

O

Solid

O

C

H

H

O

C

H

Water

H

C

H

O

H

Gas

C

N

N

H

H

O

Nitrogen

H

Examples of molecules
???
• Why is water a liquid, nitrogen a gas and glucose a solid?
• What makes a solid a solid?

a liquid a liquid?

a gas a gas?

One clue to this mystery was first reported in 1827 by scientist Robert Brown –
• Brownian Motion
The water molecules surrounding the dust particle are in constant, random motion.
• When they hit the dust particle, they push it in random directions
Matter in motion
• The idea that the particles (atoms and molecules) of all matter are in constant, random motion is called the kinetic theory of matter.
Kinetic Theory of Matter
• All matter is made of atoms and molecules.
• These particles are always in motion.
• The higher the temperature, the faster the particles move.
• At the same temperature, heavier particles move slower and lighter particles move faster.
Temperature and Heat
• What makes hot tea different from cold iced tea?
• Same particles
• movement of particles is different
• Higher temp = faster moving particles
Temperature and Heat
• Lower the temperature and the particles slow down.
• At very low temperatures the motion of the molecules is very slow.
• You cannot make things so cold that the motion completely stops,

but . . .

scientists have come close.

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

absolute zero.

Absolute zero is

- 273.15° C

You can’t get

colder than that,

no matter how

hard you try

Transfer of heat
• When hot matter touches colder matter, faster moving particles collide with slower moving particles.
• The faster moving particles give some of their energy to the slower moving particles.
Matter in the solid state
• In a solid, the particles vibrate or shake back and forth
• but do not move from their position in respect to each other.
Crystals or Crystalline Solids
• Particles of crystals are arranged in repeating geometric patterns
Diamond, a form of carbon, is also a crystalline solid.
• the crystals are shaped something like pyramids.
Non-crystalline solids
• Many solids do not form crystals.
• Their molecules do not arrange into repeating patterns
• often because they are too large.
• Examples:
• glass
• many plastics
How does a solid become a liquid?
• Start with very cold ice and gradually heat it.

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

• but still held in one position by the other molecules around it.
Keep heating your ice
• When the temperature reaches 0° C, the molecules begin to break free.
• The molecules begin to move freely around each other.
• The molecules enter the liquid state.
Melting point =

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

Temperature (C°)

60°

20°

-20°

0

Heat (kilojoules)

Temperature (C°)

60°

20°

-20°

0

Heat (kilojoules)

heat of fusion

measured in

kilojoules per kilogram

kJ/kg

heat of fusion

Temperature (C°)

Heat (kilojoules)

Water’s heat of fusion is

334 kJ/kg

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

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

a 110-story building!

Freezing
• As you know, if you can melt something, you can cool the liquid again to freeze it.
• When you cool a liquid, the particles begin to slow down.
• The attractive forces between the particles begin to catch the particles,

and crystals begin to form.

Freezing point =
• the temperature at which attractive forces trap particles in a cooling liquid and form crystals.

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

Non-crystalline solids
• Non-crystalline solids, like glass, butter or wax, do not have a definite freezing or melting point.
• If you slowly heat cold butter, it gradually gets softer and softer until it is completely liquid.