jun 2, 1809 - Dalton’s Model of the Atom (early 1800's):

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The model that was constructed based off of Dalton’s theory was called a “billiard ball” model. Dalton proposed that an atom is an invisible, indestructible, solid sphere that contains no particles. Dalton's theory was that all elements are made up of atoms, and atoms of the same element are the exact same, all of them have the same mass and behave chemically the same way. With that conclusion he believed that elements are neither created or destroyed when a chemical change takes place. He also believed that every element is characterized by its mass of the atoms that make it up. Different elements are made up of different atoms with masses and chemical properties that may be similar to other elements but they are slightly different. His final conclusion was that when atoms of two different elements joined together, it would form a compound.

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