We need myriads of chemicals for myriads of our needs. To make and use all those chemicals safely, we must know chemical as well as physical, biological, and environmental properties of substances. And, we also have to use our knowledge wisely because, while holding the incredible power that paves the way to a better living, knowledge can also be "a deadly friend if no one sets the rules"
(P. Sinfield). For example, white phosphorus can be used to make phosphoric acid, which gives soft drinks that unique tingling taste that we all enjoy, but is also used in phosphorus bombs that burn, poison, and kill people. Not only do we need to make numerous varied substances and know their properties, but we also have to set the rules for how to use these substances. 1.1.4. Matter and Substance.
If, as we said above, chemistry studies substances and their transformations, what is a substance
then? To answer this question, we first need to define matter
. Everything that has a volume and mass is matter. We are matter. Animals and trees around us are matter. Air is matter. Water is matter. Matter consists of many different substances. Well, what is not matter then? Time, friendship, love, hate, our imagination, thoughts, dreams, a smile on your face are all examples of what is not matter.
A chemical substance consists of only one type of matter and has a constant composition and characteristic properties. One type of matter means molecules
of the same type (see next subsection). For example, sugar (chemical name: sucrose) is made up of molecules of only one particular type. Sugar is a substance. Water, also a substance, is made up of identical molecules of another type. However, sugar syrup, a solution of sugar in water, cannot be called a substance because it consists of molecules of two different types, molecules of sugar and molecules of water. Sugar syrup is a mixture
of two substances.