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We will now look at some more properties (molecular size, viscosity, density, melting and boiling points, thermal expansion, thermal conductivity) in detail

The carbon atoms link together to form chains of varying lengths

The boiling point and melting point of these molecules is determined by their molecular structure, and their surface area

The more carbon atoms there are in an alkane, the greater the surface area and therefore the higher the boiling point

The melting point also increases as the number of carbon atoms in the molecule increases

there are few carbon atoms), the organic compounds are gases because the intermolecular forces are weak

As the number of carbon atoms and the molecular mass increases, the compounds are more likely to be liquids or solids because the intermolecular forces are stronger

You should see that the larger a molecule is the stronger the intermolecular forces are between its molecules

This is one of the reasons why methane () is a gas at room temperature while pentane () is a liquid and icosane () is a solid

It is partly the stronger intermolecular forces that explain why petrol (mainly octane ()) is a liquid, while candle wax () is a solid

If these intermolecular forces did not increase with increasing molecular size we would not be able to put liquid fuel into our cars or use solid candles

Compare how easy it is to pour water and syrup or honey

You can see this if you take a cylinder filled with water and a cylinder filled with glycerin

Drop a small metal ball into each cylinder and note how easy it is for the ball to fall to the bottom

In the glycerin the ball falls slowly, while in the water it falls faster

Substances with stronger intermolecular forces are more viscous than substances with weaker intermolecular forces

The solid phase is often the most dense phase (water is one noteworthy exception to this)

This can be explained by the strong intermolecular forces found in a solid

These forces pull the molecules together which results in more molecules in one unit volume than in the liquid or gas phases

The more molecules in a unit volume the denser that substance will be

Substances with weak intermolecular forces will have low melting and boiling points while those with strong intermolecular forces will have high melting and boiling points

In the experiment on intermolecular forces you investigated the boiling points of several substances, and should have seen that molecules with weaker intermolecular forces have a lower boiling point than molecules with stronger intermolecular forces

One further point to note is that covalent network structures (recall from grade that these are covalent compounds that form large networks and an example is diamond) will have high melting and boiling points due to the fact that some bonds (i.e

the strong forces between atoms) have to break before the substance can melt

Covalent molecular substances (eg water, sugar) often have lower melting and boiling points, because of the presence of the weaker intermolecular forces holding these molecules together

As the alcohol (or mercury) is heated it expands and rises up the tube

This is why when you tile a floor you have to leave gaps between the tiles to allow for expansion

It is also why power lines sag slightly and bridges have slight gaps for expansion

Heat is transferred through a substance from the point being heated to the other end

This is why the bottom of a pot gets hot first (assuming you are heating the pot on a stove plate)

In metals there are some free, delocalised electrons which can help transfer the heat energy through the metal

In covalent molecular compounds there are no free, delocalised electrons and the heat does not travel as easily through the material

Explain why the melting point of oxygen () is much lower than the melting point of hydrogen chloride

So if a substance has strong intermolecular forces, then that substance will have a high melting point

We know that stronger intermolecular forces lead to higher melting points

We also know that oxygen has weaker intermolecular forces than hydrogen chloride (induced dipole versus dipole-dipole forces)

Therefore oxygen will have a lower melting point than hydrogen chloride since oxygen has weaker intermolecular forces

Induced dipole forces are the weakest intermolecular forces and hydrogen bonding is the strongest

In order for a liquid to boil the intermolecular forces must be broken and if the intermolecular forces are very strong then it will take a lot of energy to overcome these forces and so the boiling point will be higher

Water has strong intermolecular forces (hydrogen bonds) while carbon tetrachloride only has weaker induced dipole forces

Substances with stronger intermolecular forces take longer to evaporate than substances with weaker intermolecular forces

The type of intermolecular force that can exist when sodium chloride dissolves in methanol is ion-dipole forces

The formation of these forces helps to disrupt the ionic bonds in sodium chloride and so sodium chloride can dissolve in methanol

Tumi and Jason are helping their dad tile the bathroom floor

Their dad tells them to leave small gaps between the tiles

Materials (such as tiles) expand on heating and so small gaps need to be left between the tiles to allow for this expansion

If Tumi and Jason did not leave these gaps between the tiles, the tiles would soon lift up

A beam of sunlight through a window lights up a section of the floor

You might draw a series of parallel lines showing the path of the sunlight from the window to the floor

This is not exactly accurate — no matter how hard you look, you will not find unique lines of light in the sunbeam

However, this is a good way to draw light and to model light geometrically, as we will see in this chapter.We call these narrow, imaginary lines of light light rays

Recall that light can behave like a wave and so you can think of a light ray as the path of a point on the crest of a wave.We can use light rays to model the behaviour of light relative to mirrors, lenses, telescopes, microscopes, and prisms

The study of how light interacts with materials is called optics

When dealing with light rays, we are usually interested in the shape of a material and the angles at which light rays hit it

From these angles, we can determine, for example, the distance between an object and its reflection

You have learnt about the basic properties of waves before, specifically about reflection and refraction

In this chapter, you will learn about phenomena that arise with waves in two and three dimensions: diffraction

We will also build on interference which you have learnt about previously but now in more than one dimension.

The kinetic theory of matter says that all matter is composed of particles which have a certain amount of energy which allows them to move at different speeds depending on the temperature (energy)

There are spaces between the particles and also attractive forces between particles when they come close together.Now we will look at applying the same ideas to gases.The main assumptions of the kinetic theory of gases are as follows: Gases are made up of particles (eg atoms or molecules)

The size of these particles is very small compared to the distance between the particles

The collisions between particles and the walls of the container do not change the kinetic energy of the system

The temperature of a gas is a measure of the average kinetic energy of the particles

From these assumptions we can define the pressure and temperature of any gas.PressureThe pressure of a gas is a measure of the number of collisions of the gas particles with each other and with the sides of the container that they are in.Video: 23VSTemperatureThe temperature of a substance is a measure of the average kinetic energy of the particles.If the gas is heated (i.e

the temperature increases), the average kinetic energy of the gas particles will increase and if the temperature is decreased, the average kinetic energy of the particles decreases

If the energy of the particles decreases significantly, the gas liquefies (becomes a liquid).One of the assumptions of the kinetic theory of gases is that all particles have a different speed

For an ideal gas we assume that all particles in the gas have the same speed.So for an ideal gas we can simply talk about the speed of particles

But for a real gas we must use the average speed of all the particles.Video: 23VT

In grade 10 you learnt how to calculate the molar concentration of a solution

The molar concentration of a solution is the number of moles of solute per litre of solvent ()

This is more commonly given as moles of solute per cubic decimetre of solution ().To calculate concentration we use , where is the molar concentration, is the number of moles and is the volume of the solution.Calculating molar concentrations is useful to determine how much solute we need to add to a given volume of solvent in order to make a standard solution.A standard solution is a solution in which the concentration is known to a high degree of precision

When we work with standard solutions we can take the concentration to be constant.When you are busy with these calculations, you will need to remember the following:===, therefore dividing a volume in by will give you the equivalent volume in

How much sodium chloride (in g) will one need to prepare of a standard solution with a concentration of

The volume must be converted to : To find the mass of we need the molar mass of

We can get this from the periodic table (recall from grade 10 how to calculate the molar mass of a compound).The mass of sodium chloride needed is We will now look at another use of concentration which is for titration calculations.TitrationsA titration is a technique for determining the concentration of an unknown solution

Acid-base reactions and redox reactions are both commonly used for titrations.In grade 10 you did a simple acid-base titration

Now we will look at how to calculate the concentration of an unknown solution using an acid-base titration.When performing a titration we say that the substance of unknown concentration is titrated with the standard solution

A pipette is a measuring device that is used to measure an exact amount of a liquid

If you use a pipette to add liquid to a flask then you would say that the liquid was pipetted into a flask.We can reduce the number of calculations that we have to do in titration calculations by using the following: The and are the stoichiometric coefficients of compounds A and B respectively

It was found that of the sodium hydroxide was needed to neutralise the acid

Using an acid-base titration, it was found that of this solution was able to completely neutralise of a sodium hydroxide solution

First convert the volume into :Then calculate the number of moles of sulfuric acid:Now we can calculate the concentration of the sulfuric acid:Remember that only or of the sulfuric acid solution is used.Exercise 8.2See solutions Acetylene () burns in oxygen according to the following reaction: If of acetylene gas is burnt, what volume of carbon dioxide will be produced

We first work out what mass of magnesium chloride is needed to make a solution with a concentration of

It was found that of the nitric acid was needed to neutralise the base

Write down all the information you know about the reaction, and make sure that the equation is balanced

It was found that of the phosphoric acid was needed to neutralise the base

Write down all the information you know about the reaction, and make sure that the equation is balanced

of this solution is then pipetted into a conical flask and titrated with hydrochloric acid

It is found that of the hydrochloric acid completely neutralises the antacid solution

Remember that only or of the calcium carbonate solution is used

This chapter builds on the work covered in electrostatics in grade 10

Learners should be familiar with the two types of charges and with simple calculations of amount of charge

The following list summarises the topics covered in this chapter.Coulomb's law In this part of the topic learners are introduced to Coulomb's law

This is an inverse square law and has a similar form to Newton's law of Universal Gravitation

Electric fields The concept of an electric field is introduced in this part of the chapter

Learners will see how to draw the electric field lines for different configurations of charges and will learn how to determine the magnitude of the electric field

Learners will also learn how to calculate the electric field at a point due to a number of point charges

In this chapter you will learn exactly how to determine this force and about a basic law of electrostatics.Ratio and proportion - Physical Sciences, Grade 10, Science skillsEquations - Mathematics, Grade 10, Equations and inequalitiesUnits and unit conversions - Physical Sciences, Grade 10, Science skillsScientific notation - Physical Sciences, Grade 10, Science skills

This chapter takes the ideas of magnetism and the ideas of electricity and combines them into one

The following list summarises the topics covered in this chapter.Magnetic fields are associated with current carrying wires The idea that magnetism and electricity are linked is introduced