Some molecular properties of matter
Atoms and molecules
Many of the ancient Greek philosophers believed that all substances were composed of tiny particles or atoms; but it was not until the nineteenth century that this idea developed into a useful theory for explaining some of the chemical and physical properties of matter.
In 1808, the English chemist, John Dalton, produced experimental evidence to show that chemical compounds consist of molecules which are groups of atoms of various elements united in the same simple numerical proportion. An element is a substance which cannot be split into simpler substances, while anatom is the smallest portion of an element which can take part in a chemical change. At the time of which we are speaking, scientists thought of atoms as being like tiny billiard-balls, but since then we have learned a great deal about the nature of the atoms themselves. The structure of atoms is discussed in chapter 45. In the resent chapter we shall show how the molecular theory is used in physics to explain some of the elementary properties of gases, liquids, and solids.