The Atom in Philosophy and Chemistry
- The Greek Idea
- Atomic Weights and Valency
- The Periodic Law
The Greek Idea
The ancient Greek philosophers who speculated about the nature of things suspected that the immense variety of different substances forming the world results from a combination of comparatively few simple elements. Democritus (fifth century B.C.) believed that there are four elementary substances: air, water, stone, and fire, all formed by a very large number of very small particles called atoms, i.e., "indivisibles" in Greek. The atoms of air were supposed to carry the properties of "lightness" and "dryness," the atoms of water the properties of "heaviness" and "wetness," the atoms of stone the properties of "heaviness" and "dryness," while the atoms of fire were supposed to be very mobile, "slippery, and hot." On the basis of these ideas, the Greek philosophers attempted to explain the various transformations of matter as resulting from the reshuffling of the atoms constituting matter. They believed that the material of a growing plant is composed of water and stone atoms provided by the soil and atoms of fire supplied by the rays of the sun. In modern chemical terminology, the Greek formula for wood would be SWF. The drying of wood was considered to be the escape from the wood of water atoms, SWF SF + W, and the burning of wood the decomposition of dry wood into fire atoms (flame) and stone atoms (ashes), SF F + S. Metals were considered to be the combination of stone atoms with varying amounts of fire atoms, SFn (the fire atoms were supposedly responsible for metallic glitter). Iron was supposed to be rather poor in fire atoms, but gold was considered to have the maximum amount of them. The formation of metals from ores treated in a furnace was thought to result from the union of the stone atoms of the ore and the fire atoms of the flame, S + nF SFSFn , and it seemed logical to expect that by enriching common metals like iron or copper with fire atoms, one should be able to turn them into gold. This point of view, which also prevailed in the Middle Ages, explains the incessant efforts of medieval alchemists to transform common metals into precious ones.
We know now that these views were quite wrong. The metals themselves and not their ores are elementary substances, and the process that takes place in blast furnaces does not add fire atoms to stony ores and turn them into metals but, quite on the contrary, subtracts oxygen from metallic oxides (ores) and thus liberates pure metals. Also, the material of a growing plant is obtained by the carbon dioxide (carbon + oxygen) from the air combining with the water (hydrogen + oxygen) from the soil, while the sun’s rays supply only the energy necessary for synthesizing complex organic substances from these simple ingredients. The difference between the ancient and the modern view in chemistry is shown in Figure 1.1. Although the attempted explanations were completely wrong, the idea of reducing the multitude of chemical substances to combinations of comparatively small numbers of simple elements was basically correct and now lies at the foundation of modern chemistry.
Figure 1.1. Two wrong vs. two correct views in chemistry.