Pure substances are materials that have a fixed structure and composition. For example: water and pure iron. Water is formed by oxygen and hydrogen. Both the structure and composition of oxygen and hydrogen in the water always remains. For example there are 1000 g of water, then it must be contained in 890 g of oxygen and 110 g of hydrogen. In other words, the water contains 89% oxygen and 11% hydrogen.
Similarly, the iron must contain 100% pure iron. When the iron content of only 80% or 90% it is no longer pure iron. But quite a mixture. Pure substances can be divided into two kinds, namely the elements and compounds.
To get an idea of the elements, we take water samples. Water can be broken down into two simpler substances, namely oxygen and hydrogen. However, oxygen and hydrogen itself can not be broken down into other simpler substances. Oxygen and hydrogen are examples of elements. Other elements, such as iron, gold, copper, tin, carbon, and nitrogen. So the simplest element is a substance that can not be described again.
The compound is a pure substance consisting of two or more elements joined together by chemical reactions. To be able to easily understand it, take the example of water compounds. Water is composed of the elements oxygen and hydrogen. Substance properties of water are very different from the properties of its constituent elements. At room temperature, water can be used to extinguish the fire while the oxygen and hydrogen are the opposite. Oxygen is one important component that combustion can occur, and hydrogen is flammable.