0.2 Tg physical science - chapter contexts  (Page 3/10)

For example:

• the lower the ionisation energy, the more reactive the element will be
• how to predict the charge on cations and anions by using the periodic table

Atomic combinations

This section explores the forming of new substances with new physical and chemical properties when different combinations of atoms and molecules join together. This process is called chemical bonding, one of the most important processes in chemistry. The type of bond formed depends on the elements involved. Three types of chemical bonding: covalent, ionic and metallic bonding are discussed.

Covalent bonds form when atoms of non-metals share electrons. Why and how atoms join is described and explained by using Lewis dot diagrams and Couper notation to represent the formed molecules. Names and formulae of several covalent compounds are presented.

Ionic bonds form when electrons are transferred. Ionic bonding takes place when the difference in electronegativity between the two atoms is more than1,7. The cations and anions that form attract each other with strong electrostatic forces. Details of how ionic compounds form is clarified with Lewis notation. When learners become familiar with the diagram of the crystal lattice arrangement in an ionic compound as NaCl they will be able to derive the properties of ionic compounds.

Metallic bonding is the electrostatic attraction between the positively charged atomic nuclei of metal atoms and the delocalised electrons in the metal. The unique properties of metals as a result of this arrangement are described in detail.

States of matter and the kinetic molecular theory (kmt)

Educators should not skip this section assuming that learners know the KMT because they have been exposed to it in previous grades. As an educator you should challenge the learners to move mentally between the three ways of thinking and talking about matter, as shown in the diagram above.

Use the learner’s book to revise the following concepts:

The kinetic theory of matter states 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.

States of Matter

• Matter exists in one of three states: solid, liquid and gas.

• a solid has a fixed shape and volume;
• a liquid takes on the shape of the container that it is in;
• a gas completely fills the containers that it is in.

• Matter can change between these states by either adding heat or removing heat.
• Melting, boiling, freezing, condensation and sublimation are processes that take place when matter changes state.

In Grade 10 the learners should understand chemical bonds, intermolecular forces and the kinetic theory to assist them in explaining the macroscopic properties of matter, and why substances have different boiling points, densities and viscosities.

Chemical systems

The hydrosphere

The hydrosphere is made up of freshwater in rivers and lakes, the salt water of the oceans and estuaries, groundwater and water vapour. This section deals with how the hydrosphere interacts with other global systems. On exploring the hydrosphere, an investigation is proposed and guidance is given on how to choose the site, collect, and interpret the data. The very important function that water plays on our planet is highlighted, as well as threats to the hydrosphere. To cultivate an attitude of caring and responsibility towards the hydrosphere, learners are encouraged to engage in the proposed discussions on creative water conservation and investigations: how to build dams and to test the purity of water samples. As an educator you will appreciate the hints supplied for a project on water purification.