Chapter summary

Chapter summary

Presentation: VPcyl

• All the objects and substances that we see in the world are made of matter.

• This matter can be classified according to whether it is a mixture or a pure substance.

• A mixture is a combination of two or more substances, where these substances are not bonded (or joined) to each other and no chemical reaction occurs between the substances. Examples of mixtures are air (a mixture of different gases) and cereal in milk.

• The main characteristics of mixtures are that the substances that make them up are not in a fixed ratio, these substances keep their physical properties and these substances can be separated from each other using mechanical means.

• A heterogeneous mixture is one that consists of two or more substances. It is non-uniform and the different components of the mixture can be seen. An example would be a mixture of sand and water.

• A homogeneous mixture is one that is uniform, and where the different components of the mixture cannot be seen. An example would be salt in water.

• Pure substances can be further divided into elements and compounds.

• An element is a substance that cannot be broken down into other substances through chemical means.

• All the elements are found on the periodic table. Each element has its own chemical symbol. Examples are iron (\(\text{Fe}\)), sulfur (\(\text{S}\)), calcium (\(\text{Ca}\)), magnesium \((\text{Mg}\)) and fluorine (\(\text{F}\)).

• A compound is a A substance made up of two or more different elements that are joined together in a fixed ratio. Examples of compounds are sodium chloride (\(\text{NaCl}\)), iron sulfide (\(\text{FeS}\)), calcium carbonate (\(\text{CaCO}_{3}\)) and water (\(\text{H}_{2}\text{O}\)).

• When naming compounds and writing their chemical formula, it is important to know the elements that are in the compound, how many atoms of each of these elements will combine in the compound and where the elements are in the periodic table. A number of rules can then be followed to name the compound.

• Another way of classifying matter is into metals (e.g. iron, gold, copper), metalloids (e.g. silicon and germanium) and non-metals (e.g. sulfur, phosphorus and nitrogen).

• Metals are good electrical and thermal conductors, they have a shiny lustre, they are malleable and ductile, and they have a high melting point. Metals also have a high density. These properties make metals very useful in electrical wires, cooking utensils, jewellery and many other applications.

• Matter can also be classified into electrical conductors, semi-conductors and insulators.

• An electrical conductor allows an electrical current to pass through it. Most metals are good electrical conductors.

• An electrical insulator is a non-conducting material that does not carry any charge. Examples are plastic, wood, cotton material and ceramic.

• Materials may also be classified as thermal conductors or thermal insulators depending on whether or not they are able to conduct heat.

• Materials may also be magnetic or non-magnetic. Magnetism is a force that certain kinds of objects, which are called “magnetic” objects, can exert on each other without physically touching. A magnetic object is surrounded by a magnetic “field” that gets weaker as one moves further away from the object.