1. elements are made of tiny particles called atoms
2. all atoms given element are identical
3. atoms of a given element are different from any other element
4. compounds - different atoms combined always have same relative numbers & types of atoms5. atoms are indivisible; atoms are not created or destroyed in chem reactions, just regrouped
Law of Constant Composition
A given compound always contains the same proportions (by mass) of the elements. (i.e. water always contains 8g of (8 O - oxygen) and 2.7g of ( 6 C - carbon)