Dalton's Atomic Theory

Dalton's Atomic Theory is the theory that formed the basis of our current understanding of atoms and molecules. It is, of course, now archaic, but it's principal assumptions were the foundation of modern atomic theory.

Assumptions

1. All elements are composed of small, indivisible particles called "atoms."
2. All atoms of the same element have exactly the same properties.
3. Atoms of different elements have different properties.
4. Compounds are formed when atoms are joined together. Since atoms are indivisible, they can only join together in simple, whole number ratios.