Focus 1

Question 1

Recall the definition of an atom, element, molecule, compound, and mixture and use diagrams to represent these definitions

Answer 1

An atom is the smallest unit of an element which retains the properties of that element

An element is a pure substance made up of only one type of atom

A compound is a substance that is made up of two or more elements chemically combined (bonded) in a fixed ratio – they cannot be physically separated

A molecule is the smallest structural unit of an element or compound that retains the properties of that element or compound

A mixture is a group of molecules physically combined but not chemically combined – it is an impure substance and can be physically separated

Question 2

List the key characteristics involved in a physical change and a chemical reaction

Answer 2

Physical change = change in form/state of matter & is usually reversible
e.g. water evaporating into water vapour, water freezing into ice

Question 3

List the key characteristics involved in a chemical reaction

Answer 3

Chemical change = change in the chemical makeup of a substance when substances are broken down or when new substances are formed & are usually irreversible
e.g. precipitation reactions, neutralisation reactions, combustion, etc