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Elements are made up of atoms,
the smallest particle that has any of the properties of the element.John Dalton,
in 1803, proposed a modern theory of the atom based on the following
assumptions.
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1. Matter is made up of
atoms that are indivisible and indestructible.
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2. All atoms of an element
are identical.
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3. Atoms of different
elements have different weights and different chemical properties.
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4. Atoms of different
elements combine in simple whole numbers to form compounds.
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5. Atoms cannot be created
or destroyed. When a compound decomposes, the atoms are recovered
unchanged.
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