Basically, Dalton's Atomic Theory says that different elements are made up of atoms with different weights. By mixing and matching those elements, you can get compounds. And if you want to know which elements make up a compound, you can figure it out by looking at the compound's molecular weight. Finally, when a chemical reaction occurs, the atoms themselves aren't altered. Instead, they are just rearranged into different molecules.
For a good webpage on Dalton's Atomic Theory, click here. From this you should be able to draw a picture on your own.
(republished on 07/21/06)