I feel that I understood a lot of the information and material that we covered throughout Chapter 4 "The Structure of the Atom". First we started off learning about the philosophers. Many of the early philosophers were Greek including: Democritus, Aristotle, and Dalton. Democritus's ideas were definitely a beginning point. He believed different kinds of atoms had different size and shape, different properties of matter were due to different atoms movements, and matter was composed of empty space through which atoms traveled. This ideas were rejected by Aristotle who didn't agree that empty space "nothingness" could exist. Later on Dalton created his atomic theory. He said all matter was composed of extremely small particles, all atoms were identical, atoms couldn't be created, divided, or destroyed, and in chemical reactions atoms combine, separate,or rearrange. These ideas I understood very well. I also see how the theories have changed over the years with advancements in knowledge & technology. One thing I'm having a hard time grasping is how small an atom really is. In our books it gives an example: In 2000, the world population was estimated at 6 billion. Atoms in a penny is 5 billion times as many atoms in a copper penny than humans in the world! That is a hard concept to grasp!