AIT2ANatural Science 12
ATOM DEVELOPMENT WITH SCIENTISTS INVOLVED
400 B.C. - Democritus’ atomic theory posited that all matter is made up small indestructible units he called atoms. Democritus expanded the idea 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 and weight. The differences in these characteristics explained the differences in the properties of the matter around us. Unfortunately for Democritus and mankind in general, his ideas were largely ignored for the next 2000 years.
1704 - Isaac Newton theorized a mechanical universe with small, solid masses in motion. 1803 - John Dalton proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together. While others had proposed very similar theories, John Dalton is usually credited with developing the first coherent atomic theory. Dalton's theory can be summarized as follows:
1. Matter is composed of small particles called atoms.
2. All atoms of an element are identical, but are different from those of any other element. 3. During chemical reactions, atoms are neither created nor destroyed, but are simply rearranged. 4. Atoms always combine in whole number multiples of each other. For example, 1:1, 1:2, 2:3 or 1:3 1896 - Henri Becquerel discovered radiation by studying the effects of x-rays on photographic film. In 1896, Henri Becquerel discovered that a sample of uranium was able to expose a photographic plate even when the sample and plate were separated by black paper. He also discovered that the exposure of the plate did not depend on the chemical state of the uranium (what uranium compound was used) and therefore must be due to some property of the uranium atom...