1. All matter is composed of atoms. These indivisible and indestructible objects are the ultimate chemical particles.
2. All atoms of a given element are identical, both in mass and in properties. Atoms of different elements have different masses and ifferent properties.
3. Compounds are formed by combination of two or more different kinds of atoms. Atoms combine in the ratio of small whole numbers.
4. Atoms are the units of chemical change. A chemical reaction involves only the combination, separation, or rearrangement or atoms.