1. How many times can I cut a pizza in half?

2. What is a pizza? Bread/crust Sauce Cheese If I keep cutting it in half, eventually I will have a piece that is just bread. It’s not pizza any more. It’s just bread. What if I keep cutting? Soon the pieces will be so small that I can’t tell they’re bread. I just have a piece of starch. I can break the starch into sugars. I can break the sugars into simpler sugars. What happens when I keep breaking things into smaller pieces?

3. Greek Classical Element Greek Classical Elements The ancient Greeks thought that every thing was made of different amounts of four elements: Air, Earth, Fire, and Water.

4. Chinese Classical Elements The ancient Chinese had a similar idea, but had five elements: Earth, Fire, Metal, Water, and Wood.

5. Democritus Lived 2400 years ago (~150 BE) Used the word atomos to describe the parts “I can not cut” that he thought all things were made of Thought there were many types of atoms with different properties that accounted for different kinds of matter

6. Atoms If I break a simple sugar into smaller pieces, I get what Democritus called atoma. We call these pieces atoms. There are many different kinds of atoms, but each atom is made of three kinds of smaller pieces.

7. Atoms These three pieces or particles are called protons, neutrons, and electrons. The number of each particle determines the properties of the atom.

8. Modern Elements

9. You can think of elements as different flavors of atoms. Every flavor of ice cream has different properties— different color, different taste, etc. Every element also had different properties— different color, different melting point, density, etc.

10. Reading the Periodic Table An entry on the periodic table will usually (but not always) tell you the name of the element. It will tell you the symbol for the element. It will tell you the atomic number (The number of protons in an atom of the element.)

11. Reading the Periodic Table Many Periodic Tables will also tell you the atom’s atomic mass. (Equal to the number of protons plus neutrons. But not all atoms of the same element have the same number of neutrons. Atomic mass is given as an average or as a range the average falls within.