All the objects that we see in the world around us, are made of matter. Matter makes up the air we breathe, the ground we walk on, the food we eat and the animals and plants that live around us. Even our own human bodies are made of matter!

Different objects can be made of different types of matter, or materials. For example, a cupboard (an object) is made of wood, nails and hinges (the materials). The properties of the materials will affect the properties of the object. In the example of the cupboard, the strength of the wood and metals make the cupboard strong and durable. In the same way, the raincoats that you wear during bad weather, are made of a material that is waterproof. The electrical wires in your home are made of metal because metals are a type of material that is able to conduct electricity. It is very important to understand the properties of materials, so that we can use them in our homes, in industry and in other applications. In this chapter, we will be looking at different types of materials and their properties.

Some of the properties of matter that you should know are:

The diagram below shows one way in which matter can be classified (grouped) according to its different properties. As you read further in this chapter, you will see that there are also other ways of classifying materials, for example according to whether or not they are good electrical conductors.

Figure 1: The classification of matter

We see mixtures all the time in our everyday lives. A stew, for example, is a mixture of different foods such as meat and vegetables; sea water is a mixture of water, salt and other substances, and air is a mixture of gases such as carbon dioxide, oxygen and nitrogen.

Definition 1: Mixture

A mixture is a combination of two or more substances, where these substances are not bonded (or joined) to each other.

In a mixture, the substances that make up the mixture:

Some other examples of mixtures include blood (a mixture of blood cells, platelets and plasma), steel (a mixture of iron and other materials) and the gold that is used to make jewellery. The gold in jewellery is not pure gold but is a mixture of metals. The amount of gold in the jewellery is measured in karats (24 karat would be pure gold, while 18 karat is only 75% gold).

We can group mixtures further by dividing them into those that are heterogeneous and those that are homogeneous.

Activity: Classifying materials

Look around your classroom or school. Make a list of all the different materials that you see around you. Try to work out why a particular material was used. Can you classify all the different materials used according to their properties? On your way to school or at home or in the shops, look at the different materials that are used. Why are these materials chosen over other materials?

Activity: Making mixtures

Make mixtures of sand and water, potassium dichromate and water, iodine and ethanol, iodine and water. Classify these as heterogeneous or homogeneous. Try to make mixtures using other substances. Are the mixtures that you have made heterogeneous or homogeneous? Give reasons for your choice.

Any material that is not a mixture, is called a pure substance. Pure substances include elements and compounds. It is much more difficult to break down pure substances into their parts, and complex chemical methods are needed to do this.

One way to determine if a substance is pure is to look at its melting or boiling point. Pure substances will have a sharply defined melting or boiling point (i.e. the melting or boiling point will be a single temperature rather than a range of temperatures.) Impure substances have a temperature range over which they melt or boil. We can also use chromatography to determine if a substance is pure or not. Chromatography is the process of separating substances into their individual components. If a substance is pure then chromatography will only produce one substance at the end of the process. If a substance is impure then several substances will be seen at the end of the process.

Activity: Smartie chromatography

You will need filter paper (or chromatography paper), some smarties in different colours, water and an eye dropper.
Place a smartie in the center of a piece of filter paper. Carefully drop a few drops of water onto the smartie. You should see rings of different colour forming around the smartie. Each colour is one of the individual colours that are used to make up the colour of the smartie.

Compounds

A compound is a chemical substance that forms when two or more elements combine in a fixed ratio. Water (H2OH2O), for example, is a compound that is made up of two hydrogen atoms for every one oxygen atom. Sodium chloride (NaClNaCl) is a compound made up of one sodium atom for every chlorine atom. An important characteristic of a compound is that it has a chemical formula, which describes the ratio in which the atoms of each element in the compound occur.

Definition 5: Compound

A substance made up of two or more elements that are joined together in a fixed ratio.

Figure 2 might help you to understand the difference between the terms element, mixture and compound. Iron (Fe) and sulphur (S) are two elements. When they are added together, they form a mixture of iron and sulphur. The iron and sulphur are not joined together. However, if the mixture is heated, a new compound is formed, which is called iron sulphide (FeS). In this compound, the iron and sulphur are joined to each other in a ratio of 1:1. In other words, one atom of iron is joined to one atom of sulphur in the compound iron sulphide.

Figure 2: Understanding the difference between a mixture and a compound

Figure 2 shows the microscopic representation of mixtures and compounds. In a microscopic representation we use circles to represent different elements. To show a compound, we draw several circles joined together. Mixtures are simply shown as two or more individual elements in the same box. The circles are not joined for a mixture.

We can also use symbols to represent elements, mixtures and compounds. The symbols for the elements are all found on the periodic table. Compounds are shown as two or more element names written right next to each other. Subscripts may be used to show that there is more than one atom of a particular element. (e.g. H2OH2O or NaClNaCl). Mixtures are written as: a mixture of element (or compound) A and element (or compound) B. (e.g. a mixture of FeFe and SS).

One way to think of mixtures and compounds is to think of buildings. The building is a mixture of different building materials (e.g. glass, bricks, cement, etc.). The building materials are all compounds. You can also think of the elements as Lego blocks. Each Lego block can be added to other Lego blocks to make new structures, in the same way that elements can combine to make compounds.

Exercise 2: Mixtures and pure substances

For each of the following substances state whether it is a pure substance or a mixture. If it is a mixture, is it homogenous or heterogenous? If it is a pure substance is it an element or a compound?

1. Blood
2. Argon
3. Silicon dioxide (SiO2SiO2)
4. Sand and stones

Solution

1. Blood is a mixture since it is made up of many different compounds and substances. Blood is a homogenous mixture since you cannot see the individual components and the components are uniformly distributed.
2. Argon is a pure substance. Argon is an element since we can find it on the periodic table.
3. Silicon dioxide is a pure substance. It is a compound since it is made of the elements silicon and oxygen joined in a fixed ratio.
4. Sand and stones form a mixture. There are two distinct compounds. It is a heterogenous mixture since the particles are not uniformly distributed and we can see the individual pieces.

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Activity: Using models to represent substances

Use coloured balls and sticks to represent elements and compounds. Some examples that you can try to build are:

• Hydrogen
• Oxygen
• Nitrogen
• Neon
• Sodium chloride (salt, NaClNaCl)
• Potassium permanganate (KMnO4KMnO4)
• Water (H2OH2O)
• Iron sulphide (FeSFeS)

Think about the way that we represent substances microscopically. Would you use just one ball to represent an element or many? Why?

Elements, mixtures and compounds

1. In the following table, tick whether each of the substances listed is a mixture or a pure substance. If it is a mixture, also say whether it is a homogeneous or heterogeneous mixture.

   Table 1

   Substance	Mixture or pure	Homogeneous or heterogeneous mixture
   fizzy colddrink
   steel
   oxygen
   iron filings
   smoke
   limestone (CaCO3CaCO3)

   Click here for the solution
2. In each of the following cases, say whether the substance is an element, a mixture or a compound.
   1. CuCu
   2. iron and sulphur
   3. AlAl
   4. H2SO4H2SO4
   5. SO3SO3
   Click here for the solution

Think about what you call your friends. Their full name is like the substances name and their nickname is like the substances formulae. Without these names your friends would have no idea which of them you are referring to. In the same way scientists like to have a consistent way of naming things and a short way of describing the thing being named. This helps scientists to communicate efficiently.

It is easy to describe elements and mixtures. We simply use the names that we find on the periodic table for elements and we use words to describe mixtures. But how are compounds named? In the example of iron sulphide that was used earlier, which element is named first, and which 'ending' is given to the compound name (in this case, the ending is -ide)?

The following are some guidelines for naming compounds:

The above guidelines also help us to work out the formula of a compound from the name of the compound.

When working out the formula of a compound from the name we work backwards. For example, if you are given potassium chloride and were told to give its formula you would start by noting that we having potassium and chloride. Next you write down the formula for each of these ions. Potassium is K+K+ and chloride is Cl-Cl-. The final step is to note the charge on each ion to see how it combines. Since both potassium and chlorine have a charge of 1, they combine in a 1:1 ratio. The formula is KClKCl.

We can use these rules to help us name both ionic compounds and covalent compounds (more on these compounds will be covered in a later chapter). However, covalent compounds are often given other names by scientists to simplify the name (or because the molecule was named long before its formula was discovered). For example, if we have 2 hydrogen atoms and one oxygen atom the above naming rules would tell us that the substance is dihydrogen monoxide. But this compound is better known as water! Or if we had 1 carbon atom and 4 hydrogen atoms then the name would be carbon tetrahydride, but scientists call this compound methane.

The elements in the Periodic Table can also be divided according to whether they are metals, metalloids or non-metals. On the right hand side of the Periodic Table you can draw a 'zigzag' line (This line starts with Boron (BB) and goes down to Polonium (PoPo). This line separates all the elements that are metals from those that are non-metals. Metals are found on the left of the line, and non-metals are those on the right. Along the line you find the metalloids. You should notice that there are more metals then non-metals. Metals, metalloids and non-metals all have their own specific properties.

You should now be able to take any material and determine whether it is a metal, non-metal or metalloid simply by using its properties.