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History of the Atom 1
The History of the Atom
Democritus had the idea that state that matter was composed of small particles called
"atoms" that could be divided no further. These atoms were all composed of the same
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 his ideas were ignored for the next 2000
years until Dalton continued his studies.
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
3) During chemical reactions, atoms are neither created nor destroyed, but are
While writing a textbook for his chemistry students Dmitri Mendeleev attempted to
classify the elements. He used the only unchanging numerical data available at this time
which was the atomic weight. By arranging the elements in order of increasing atomic
weight he discovered that there existed a periodicity of the elemental properties. He
used this periodicity to create a table in which that elements with similar properties
were vertically aligned with each other.