Democritus of Abdera

Our senses suggest that matter is continuous. The air that surrounds us, for example, feels like a continuous fluid. (We do not feel bombarded by individual particles in the air.) The water we drink looks like a continuous fluid. (We can take a glass of water, divide it in halves, and repeat this process again and again, without appearing to reach the point at which it is impossible to divide it one more time.)

Because our senses suggest that matter is continuous, it isn't surprising that the debate about the existence of atoms goes back as far as we can trace and continued well into this century. The first proponents of an atomic theory were the Greek philosophers Democritus, and his student Leucippus, The first Atomists, who proposed the following model in the fifth century B.C.

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Democritus (and Leucippus) suggested that:

1. Matter is composed of atoms separated by empty space through which the atoms move.

2. Atoms are solid, homogeneous, indivisible, and unchangeable.

3. All apparent changes in matter result from changes in the groupings of atoms.

4. There are different kinds of atoms that differ in size and shape.

5. The properties of matter reflect the properties of the atoms the matter contains.