We think you are located in South Africa. Is this correct?

Success in Maths and Science unlocks opportunities

Chapter summary

Presentation: VPdvy

• The smallest unit of matter is the atom. Atoms can combine to form compounds.

• A compound is a group of two or more different atoms that are attracted to each other by relatively strong forces or bonds. The atoms are combined in definite proportions.

• In a compound, atoms are held together by chemical bonds. Covalent bonds, ionic bonds and metallic bonds are examples of chemical bonds.

• A covalent bond exists between non-metal atoms. An ionic bond exists between non-metal and metal atoms and a metallic bond exists between metal atoms.

• Covalent molecular structures interact and exist as separate molecules.

• Network structures exist as giant repeating lattices. Network structures can consist of covalent, ionic or metallic compounds.

• A chemical formula is an abbreviated (shortened) way of describing a compound.

• The molecular formula is a concise way of expressing information about the atoms that make up a particular covalent molecular compound. The molecular formula gives the exact number of each type of atom in the molecule.

• The empirical formula is a way of expressing the relative number of each type of atom in a chemical compound. The empirical formula does not show the exact number of atoms, but rather the simplest ratio of the atoms in the compound.

• The structure of a compound can be represented by stick, ball-and-stick or space-filling models.

• A stick model use coloured sticks to represent compounds.

• A ball-and-stick model is a 3-dimensional molecular model that uses “balls” to represent atoms and “sticks” to represent the bonds between them.

• A space-filling model is also a 3-dimensional molecular model. The atoms are represented by spheres.