The Atom: All of the matter around us is made of atoms, the chemical building blocks of our world.
The Greek Atom:
In about 530 B.C.E., a group of Greek philosophers, the most famous of whom was a man named Democritus, gave this question some serious thought. Democritus, argued (purely on philosophical grounds) that if you took the world's sharpest knife and started slicing chunks of matter, you would eventually come to the smallest piece piece that could not be divided further. He called this smallest piece the “atom,” which translates roughly as “unquotable.” He argued that all material was formed from these atoms, and that the atoms are eternal and unchanging, but that the relationship between the atoms is constantly shifting.
These Greeks philosophers did not really engaged in science-- their reasoning lacked the interplay between observation and hypothesis that characterizes the scientific method. It was not until the beginning of the nineteenth century that the modern theory of atoms was born.
The Beginning of an Atomic Theory:
Modern atomic theory is generally attributed to an English meteorologist, John Dalton (1766-1844). In 1808, Dalton published a book called New System of Chemical Philosophy, in which he argued that the new knowledge being gained by chemists about materials provide evidence, in and of itself, that matter was composed of atoms. The argument went something like this: Chemists knew that most materials can be broken down into simpler chemicals. If you burn wood, for example, you get carbon dioxide, water and all sorts of materials in the ash. If you use an electric current to break down water, you get two gasses, hydrogen and oxygen. In addition, no matter how much of a material you break down, it always breaks down in the same proportion. Water, for example, always yields one part hydrogen and to eight parts of oxygen by weight.
On the other hand, a few materials could not be broken down into other things. Chemists could heat wood to get charcoal (essentially pure carbon), for example: but, try as they might,they could not break the carbon down any further. Such seemingly indivisible materials were called chemical elements.
The hypothesis that we now call atomism was very simple. Dalton suggested that for each chemical element there was a corresponding species of indivisible objects called atoms. He borrowed the name from the Greeks but very little else. Two or more atoms stuck together from a molecule--- the same term applies to any cluster of atoms that can be isolated, whether it contains two atoms or a thousand. Molecules make up most of the different kinds of materials we see around us. Water, for example, forms from one oxygen atom and two hydrogen atoms (this, the familiar H2O).
In Dalton's view, atoms were truly indivisible--he thought of them as little bowling balls. In Dalton's world, them indivisible atoms provided the fundamental building blocks of matter.
This picture was not only intellectually attractive, but it also conformed to much of what chemical had discovered by Dalton's time. For example, it explained why chemical elements could not be broken down--they were made from a single type of atom that was, by definition, indivisible. It also explained the regular proportions of elements in compounds, such as the one-to-eight ratio of hydrogen to oxygen in water. Because of these successes, scientists rapidly accepted the atomic picture, which became a part of the way we think about the world. Even though we know today that atoms are made up of even smaller parts, we still use the old name “atom” for historical reasons.
