Chemistry can be defined as the study of matter. Matter is anything that occupies space, from very small things like electrons to very large things like stars.

All matter can be broken down into the small parts that make it up. The element is the basic unit of matter; it is a substance that cannot be broken down into simpler substances by any chemical means. 109 elements have been identified so far. 90 of them were first found in nature; the rest were made in laboratories. Different combinations of these elements make up every single object in the universe. Some well-known elements are carbon, oxygen, iron, mercury, and gold.

Each element is made up of one kind of atom. It is hard to imagine how small atoms are. There are more than 1,000,000,000,000,000,000,000 - that's one sextillion - atoms in a single drop of water! Even though atoms are that small, they are made up of even smaller parts. Atoms are composed of protons, neutrons, and electrons.

The number of protons, neutrons, and electrons an atom has determines its characteristics, or properties. Physical properties are characteristics, such as colour, density, and hardness, that let us describe a substance. Chemical properties describe the way in which a substance can change or combine with other substances.

Modern chemistry is a pretty new science. It developed in the late seventeenth century. (Compare this to biology which has existed for thousands of years.) Modern chemistry was born out of alchemy, which was a mixture of philosophy, astrology, magic, chemistry, and other ingredients. Alchemists are famous for trying to find the Philosophers' Stone which could turn any worthless metal into gold. One of the first modern chemists was Robert Boyle. Boyle insisted that chemistry should perform controlled experiments and make measurements. This vision that he described in the late seventeenth century laid the foundation for the chemistry that is still being practiced today.