What Is an Element?
An element is any substance whose molecules cannot be broken up and made to form other substances. You can take one or more elements and make a compound, which is what water is. A compound is a substance in which the molecules are made up of at least two kinds of elements or elementary substances.
THE DIFFERENCE BETWEEN ELEMENTS AND COMPOUNDS
The things we find in the world are known as either compounds or elements. An element, as we have already learned, is something in which the molecules cannot be broken up. A compound is, therefore, a substance in which the molecules are made of molecules of one or more elements and is either gas, liquid or solid, according to the relations which these molecules have to each other. We have so far discovered less than eighty real elements in the world, although since we find a new one every little while, there are probably many more as yet undiscovered.
Not all elements are gases, of course. Solids like copper, gold, iron, lead and a number of others are elements. Among liquids we have mercury, and of the gases we find hydrogen, nitrogen and oxygen, which are the three wonderful gases about which we are about to learn something, and these three are also the world’s most important gases. Ammonia is an element, but, while we think of it as a liquid, the real ammonia is really a gas. Our household ammonia is really a compound of ammonia with something else.