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 Atomic Theory is the theory of the structure, properties, and behavior of the
atom. Many changes, modifications, additions, and deletions have been made since
Democritus first proposed the atomic theory in 400 B.C. The most notable of
these changes is Dalton's theory. Our conception of the atom today is
based on three main points.
- Each chemical element is made up of very small particles called atoms.
- All of the atoms of a given element are identical. The atoms of one
element are different from the atoms of any other element in some
fundamental way.
- Atoms combine with each other to form compounds. A given compound always
has the same relative numbers of different types of atoms.
This theory explains three fundamental laws.
- The Law of Conservation of Mass (Antoine Lavoisier):
The total mass of the products will always be equal to the total mass of the reactants in any
chemical reaction.
- The Law of Definite Proportions (Joseph Proust):
In every pure compound the mass ratios of the elements that make it up are
constant.
- The Law of Multiple Proportions (John Dalton):
When a fixed amount of one element combines with another element to form two
or more compounds, the amounts of the second element are always in a ratio
of small whole numbers.
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