TABLE OF CONTENTS It has been hypothesized for millennia that all matter is made of tiny, indivisible, smallest bits of matter called atoms. Great progress had been made during the nineteenth century in attributing the thermodynamic laws and some of the properties of matter, especially gases, to the kinetic-molecular theory (Chapter 7). In addition, it was known for centuries that there are different types of so-called fundamental "elements" in nature gold, silver, copper, sodium, etc. There are the smallest units into which substances can be divided by chemical means. Eventually it was found useful to give the elements special symbols, for example, "C" for carbon, "O" for oxygen, "H" for hydrogen, and so on.
For many people, such as the English chemist John Dalton (1766 1844), these different elements indicated that nature is also made up of different types of atoms, one type of atom for each element. Each element was considered a collection of identical, indestructible atoms, and this idea was confirmed in chemical studies during the nineteenth century. When two or more atoms link together, they form a molecule. The molecule may be an element itself if both atoms are the same, such as O 2, or it may be a compound if the atoms are different, such as H 2O. Since atoms are not divisible, the idea of joining two atoms of hydrogen to, say, 1 atoms of oxygen instead of exactly one atom of oxygen is meaningless. Dalton's law of fixed proportions follows quite naturally...
