Contains the full lesson along with a supporting toolkit, including teachers’ notes.
A Little Background
From earliest times as people observed the world around them; they classified plants, animals and minerals on the basis of similar characteristics. They also wondered what materials were made of and a widespread belief emerged that they were composed of various combinations of earth, air, fire and water. To these four 'elements' a fifth was sometimes added, especially in some eastern cultures; it was described as essence, quintessence, aether or space and was regarded as a nonmaterial aspect of things.
The Modern Ideas of 'Element'
As people discovered how to extract metals from their ores and began analysing many naturally occurring substances the ancient ideas became less useful. Newer ideas gradually emerged and in 1661 Robert Boyle in his book The Sceptical Chymist proposed a more modern concept of elements. By 1810 the chemical composition of many substances was well established.
Elements and Compounds
We now consider a substance to be an element if it is not composed of other substances. Compounds are composed of two or more elements, not just mixed together but bound together so as to form a new substance with (usually) completely different properties from those of the elements it contains. For example, water is a compound of hydrogen and oxygen; its properties are completely different from those of either hydrogen or oxygen.