DEMOCRITUS
Lived from: 460-370 BC
Put forward atomic model in: 442 BC
Description of his model:
Democritus’s model stated that matter consists of invisible particles called atoms and a void (empty space). He stated that atoms are indestructible and unchangeable. Also that they are homogenous, meaning they have no internal structure. His atomic model was solid, and stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them.
Lived from: 460-370 BC
Put forward atomic model in: 442 BC
Description of his model:
Democritus’s model stated that matter consists of invisible particles called atoms and a void (empty space). He stated that atoms are indestructible and unchangeable. Also that they are homogenous, meaning they have no internal structure. His atomic model was solid, and stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them.
More Information:
Democritus, a Greek who lived from 460 BCE to 370 B.C., developed a new theory of matter; his ideas were based on reasoning rather than science, and drew on the teachings of two Greek philosophers who came before him: Leucippus and Anaxagoras.
Democritus knew that if you took a stone and cut it in half, each half had the same properties as the original stone. He reasoned that if you continued to cut the stone into smaller and smaller pieces, at some point you would reach a piece so tiny that it could no longer be divided.
Democritus called these infinitesimally small pieces of matter atomos, meaning "indivisible." He suggested that atomos were eternal and could not be destroyed. Democritus theorized that atomos were specific to the material that they made up, meaning that the atomos of stone were unique to stone and different from the atomos of other materials, such as fur. This was a remarkable theory that attempted to explain the whole physical world in terms of a small number of ideas.
Democritus, a Greek who lived from 460 BCE to 370 B.C., developed a new theory of matter; his ideas were based on reasoning rather than science, and drew on the teachings of two Greek philosophers who came before him: Leucippus and Anaxagoras.
Democritus knew that if you took a stone and cut it in half, each half had the same properties as the original stone. He reasoned that if you continued to cut the stone into smaller and smaller pieces, at some point you would reach a piece so tiny that it could no longer be divided.
Democritus called these infinitesimally small pieces of matter atomos, meaning "indivisible." He suggested that atomos were eternal and could not be destroyed. Democritus theorized that atomos were specific to the material that they made up, meaning that the atomos of stone were unique to stone and different from the atomos of other materials, such as fur. This was a remarkable theory that attempted to explain the whole physical world in terms of a small number of ideas.
Ultimately, though, Aristotle and Plato, two of the best-known philosophers of Ancient Greece, rejected the theories of Democritus. Aristotle accepted the theory of Empedocles (Empedocles argued that all matter was composed of four elements: fire, air, water, and earth. The ratio of these four elements affected the properties of the matter). Aristotle added his own (incorrect) idea that the four core elements could be transformed into one another.
Because of Aristotle's great influence, Democritus' theory would have to wait almost 2,000 years before being rediscovered.
Summary:
The goal of the Greek philosophers was to explain the natural world. Coming to the conclusion of the phenomena they observed, that a single "primary matter" existed. It was of this primary matter, modified in various ways, that all other things were created.
Democritus expanded this theory to state that matter was composed of small particles called "atoms" that could be divided no further. These atoms were all composed of the same primary matter with the only differences between them being their size, shape, mass, positions and arrangement. The differences in these characteristics explained the differences in the properties of the matter around us.
Adapted from: Atomic Theory and Structure Early Ideas about Matter: From Democritus to Dalton by Anthony Carpi, Ph.D.
http://www.visionlearning.com/en/library/Chemistry/1/Early-Ideas-about-Matter/49