PARTICLE THEORY

OR KINETIC THEORY OF MATTER

HOW TO DEAL WITH THINGS WE DON’T REALLY SEE!!

OBSERVATION OF MATTER

Dealing with the mAcroscopic world

We can even have some magnification

If we want to have a more detailed view we need to enter the mIcroscopic world

We can see photons, but we can’t see X-rays. And, in the end we have our eyes to see.

So, we have to see “indirectly”. We have to make visible what is not

And seeing “indirectly” means interpreting: “translating” what our eyes can’t see into something our eyes can see and our brain is able to understand.

And this can be complicated and, sometimes, a bit confusing

Remember the definition I gave you at the very beginning ...

Definition It is the study of MATTER, what it is made of,

how it behaves, and the changes it is subjected to.

It trys to observe phenomena and explain them through laws that can be applied to the world around us.

How to travel from the MACROSCOPIC to the

MICROSCOPIC world without getting lost?

MIXTURES Pure Substances

Matter surrounds us mainly in the form of mixtures.

But we’ll have to do something to obtain :

Once we have obtained pure

substances out of the mixtures, we can go on studying this type

of substance s to classify and

characterize them.

To study MATTER (Mixtures and Pure Substances) we’ll have to construct MODELS.

These models always do some simplifications to help us understand how matter is and why it behaves the way it does.

The first model we have to consider is : The particle theory

(or kinetic theory of matter)

Particle theory helps to explain properties and behaviour of materials by providing a model which enables us to visualise what is happening on a very small scale inside those materials. As a model it is useful because it appears to explain many phenomena but as with all models it does have limitations.

The model can be used to help explain:1.- The properties of matter 2.- What happens during physical changes such as melting, boiling and evaporating.3.- What temperature is.4.- What pressure of gas in a container is.

And what does this theory say?

It says that all matter consists of many, very small particles which are constantly moving. The degree to which the particles move is determined by the amount of energy and the forces of attraction with other particles. The forces between particles are always attractive. The closer the particles, the stronger the force.

So, we just have to move in the MICROSCOPIC 1 level !

This theory explains the three states of matter: solid, liquid and gas. Doesn’t it?

Yes, but it refers to pure substances in the forms of solid, liquid and gas.

I know it’s difficult to try and find pure substances at home !!

Even bottled water is not a pure substance (from the microscopic 1 point of view) !!

Let’s put our microscopic 1 glasses on to see how matter looks like

Pure substance: Made out of 1 and only type of particle.

The state of aggregation (solid, liquid or gas) will determine the arrangement of the particles

Mixture: Made out of more than one type of particle.

The state of aggregation (solid, liquid or gas) will determine the arrangement of the particles

??

MIXTURE OF TWO GASES

PURE SOLID SUBSTANCE

Pure sugar

Sugar dissolved in water

Pure air

Remember that it is very important to know the point of view we take.

In the MACROSCOPIC level of observation we can’t talk about PARTICLES.

PARTICLES ARE WHAT WE SAY MATTER IS MADE OUT OF.

AN ENORMOUS SET OF PARTICLES IS WHAT OUR EYES CAN SEE AND OUR HANDS CAN HANDLE.

AN INCREDIBLE NUMBER OF PARTICLES OF EACH PURE SUBSTANCE IS WHAT GIVES THIS SUBSTANCE ITS MACROSCOPIC PROPERTIES. THIS MACROSCOPIC PROPERTIES DEPEND ON MANY TYPES OF MICROSCOPIC INTERACTIONS

Draw this substance from the MACROSCOPIC POINT OF VIEW

But first you have to know that: Square: is for an olive oil particle

Circle: is for a water particleTriangle: is for a salt particle

Salt is soluble in water (not in olive oil)Oil and water do not mix

From the MACROSCOPIC POINT OF VIEW:

This piece of matter is a mixture because we

are able to see two different substances.

We do not see the salt dissolved in water

Draw this substances from the MACROSCOPIC POINT OF VIEW

These two gasesare completely mixed,

they both are transparent and they

are closed in a transparent container

This is a yellow substance

From the MACROSCOPIC POINT OF VIEW:

This piece of matter is not a mixture to our

eyes because we can only see two one

“homogeneous” thing

We may know that this is a glass with saltwater, but ...

A way to tell a PURE substance from a MIXTURE (from the macroscopic point of view) is … to measure its properties

ONLY PURE SUBSTANCES HAVE FIXED PHYSICAL

AND CHEMICAL PROPERTIES.

PURE WATER SOLIDIFIES

AT 0º C.

WATER WITH SALT DISSOLVED IN IT

SOLIDIFIES AT A LOWER TEMPERATURE

Physical Properties • physical property - characteristic of a

pure substance that you can observe or measure without changing the identity of the substance.

• Examples: color, density, melting point, boiling point, heat capacity (?)

REMEMBER THAT ONLY PURE SUBSTANCES HAVE FIXED

PROPERTIES.

WATER IS THE PURE SUBSTANCE WITH THIS SET OF PROPERTIES:

.- Density : 1g / mL

.- Melting point: 0º C (at 1 atm)?

.- Boiling point: 100 ºC at (1 atm)?

.- Heat capacity: 4,18 J/ g K

.- Refractive index: 1,33

Melting and boiling point are physical properties. Different PURE substance will have different melting and boiling points.

The state of aggregation (solid, liquid or gas) of a PURE substance depends on: .- The substance itself..- The melting and boiling point of the substance..- The temperature the substance is at.

0ºC 100ºC

M.P. B.P

SOLID LIQUID GAS

-114,1ºC 78,5ºC

M.P. B.P

SOLID LIQUID GAS

You can repeat this drawing for any substance (provided you know its

boiling and melting points).

0ºC 100ºC

CONCLUDING:

A substance is in the solid state if its temperature is lower than its melting point.

This substance will be in the liquid state if its temperature is in between its melting and boiling points.

And the substance will be in the gas state for temperatures higher than its boiling point.

Imagine you live on a planet where only six substances exist: Ammonia, nitrogen, methane, neon, hydrogen and water. In the table below the information of their melting and boiling points can be found. The temperature of the planet is -173 ºC. What is the state of each substance at this temperature.

Melting point (º C) Boiling point (º C) State at -173 º C

Ammonia -73 -33

Nitrogen -209,8 -194,8

Methane -184 -161

Neon -248,5 -245,8

Hydrogen -259 -252,6

Water 0 100

SOLID

SOLID

LIQUID

GAS

GAS

GAS

But, what the state of each substance is here on planet earth at 15ºC???

Melting point (º C) Boiling point (º C) State at 15 º C

Ammonia -73 -33

Nitrogen -209,8 -194.8

Methane -184 -161

Neon -248,5 -245,8

Hydrogen -259 -252,6

Water 0 100

GAS

LIQUID

GAS

GAS

GAS

GAS

AND WE CAN LINK THE MICROSCOPIC WITH THE MACROSCOPIC WORLD

-114,1ºC 78,5ºC

M.P. B.P

SOLID LIQUID GAS

0ºC 100ºC

TEMPERATURE

HEAT

Internal energy is related to the TOTALenergy within an object.

Particles in a substance have manytypes of energy (kinetic, potential,

vibrational, rotational, and many more)

Internal energy and temperature are notthe same thing, though they are related.

But they are at the same temperature

50 degrees C 20 degrees C

50 degrees C 20 degrees C

Heat

HEAT : IS ENERGY IN TRANSFER DUE TO A DIFFERENCE IN

TEMPERATURE.

50 degrees C 20 degrees C

Heat

Heat FLOWS from the HOT substance to the COOL one

spontaneously

• Energy always moves from:

HOT object COOLER object

Cup of water at 20 °C in a room at 30°C - gains heat energy and heats up – its temperature rises.Cup of water at 20 °C in a room at 10°C loses heat energy and cools down – its temperature will fall.

The temperature of a substance depends on the speed and mass (KINETIC ENERGY) of the particles of a substance.

Even in a extremely small piece of matter there are millions of millions of millions of particles. These particles are always moving (or vibrating)

Imagine a glass of water. Particles of water move; but Imagine a glass of water. Particles of water move; but they don’t move at the same speed. There are particles they don’t move at the same speed. There are particles of water moving faster than others. If we could of water moving faster than others. If we could measure the speed of each particle, calculate the measure the speed of each particle, calculate the kinetic energy of each particle and then calculate the kinetic energy of each particle and then calculate the average kinetic energy of the particles of the average kinetic energy of the particles of the substance we would be calculating the temperature of substance we would be calculating the temperature of the substance.the substance.

But it is easier to use a thermometer, isn’t it?

How do we measure temperature?

How a thermometre works?

How does the thermometer know how hot the substance is?

The PARTICLES of the substance bump into the thermometer and transfer energy. How often and how hard they bump into the thermometer are directly related to their speed. Temperature turns out to be related to the average speed of the molecules in a substance.

TEMPERATURE.- It is a property that can be measured (ºC (Celsius, centigrade) , º F (Farenheit) , K (Kelvin)

.- It can give us information about the ENERGY within the system (substance). INTERNAL ENERGY.

.- It is an average speed of molecular movement

HEATIt is ENERGY flowing from a hot body (substance) to a cooler one (The other way round is not possible)