2. HOW DO WE KNOW WHAT ATOMS LOOK LIKE? Write down the stuff in yellow.

3. TIMELINE 400 B.C. 1805 1897 1904 1911 1913 1923 1930s Today write these dates down the left side of a new page – skip lines:

4. MAKE AN ENTRY NEXT TO EACH DATE. DRAW A PICTURE OF THE ATOMIC MODEL AT EACH STAGE, TO THE FAR RIGHT OF THE CORRESPONDING DATE.

5. PEOPLE HAVE ALWAYS BEEN INTERESTED IN WHAT ALL OF THIS "STUFF" IS MADE OF. What makes a tree different from water or rocks? What does all this matter have in common?

6. ABOUT 400 BC, DEMOCRITUS THOUGHT THAT THE UNIVERSE WAS MADE OF EMPTY SPACE AND TINY BITS OF STUFF. HE THOUGHT THAT THESE BITS OF STUFF WERE SO TINY THAT THEY COULDN'T BE CUT ANY SMALLER, SO THE GREEKS NAMED THEM "ATOMS." ATOM MEANS "CANNOT BE DIVIDED" IN GREEK.

7. Add this to your timeline: 400 B.C. Matter is made of atoms

8. DEMOCRITUS' IDEA THAT MATTER IS MADE UP OF TINY PARTICLES AND EMPTY SPACE WAS A GOOD START, BUT MANY QUESTIONS STILL NEEDED TO BE ANSWERED…

9. LOADING…PLEASE WAIT not much happening on the atomic theory front for the next 300 years…

10. IN THE 1700 S, SCIENTISTS STARTED CONDUCTING ACTUAL EXPERIMENTS DEALING WITH MATTER, BUT THEY STILL WONDERED WHAT ATOMS ACTUALLY LOOKED LIKE.

11. HOW CAN YOU KNOW ABOUT SOMETHING YOU CAN’T SEE? Try making your own inferences by using models.

12. 1- EXAMINE THE “ATOMS” ON YOUR TABLE USING YOUR SENSES. WHAT MAKES ONE DIFFERENT FROM ANOTHER?

13. 2- NOW USE SOME TECHNOLOGY TO HELP YOU MAKE OBSERVATIONS. WHAT MAKES ONE ATOM DIFFERENT FROM ANOTHER?

14. UNDER YOUR TIMELINE, WRITE THIS “BIG IDEA.” We have a better model of the atom today than in the past because we have better technology.

15. In 1805, a British chemist named John Dalton did experiments which showed that each element is made of atoms, and that all atoms are alike, except that different elements have different masses. Ooooh, that’s heavy!

16. Add this to your timeline: 1805 Elements have different masses H C

17. NINETY YEARS LATER, J.J. THOMPSON BUILT ON DALTON'S IDEAS AND CONDUCTED EXPERIMENTS WHICH SHOWED THAT ATOMS HAD NEGATIVE CHARGED PARTICLES THAT HE NAMED "ELECTRONS."

18. THOMPSON'S MODEL WAS SORTA LIKE A BLUEBERRY MUFFIN. THE ATOM-MUFFIN HAD ELECTRON-BLUEBERRIES SCATTERED THROUGHOUT THE ATOM AND ALSO STUCK TO THE OUTSIDE.

19. Add this to your timeline: 1897 Atoms have negative electrons

20. IN 1904, A JAPANESE PHYSICIST NAMED NAGAOKA BUILT ON THE WORK OF THOMPSON AND DALTON. HIS EXPERIMENTS SHOWED THAT THE ELECTRONS WERE ORBITING AROUND OUTSIDE OF THE POSITIVELY CHARGED NUCLEUS

21. Add this to your timeline: 1904 Electrons are on outside of nucleus The nucleus has a positive charge

22. UNDER YOUR TIMELINE, WRITE THIS “BIG IDEA.” Scientists base their experiments on the work of others who came before. These experiments give us EVIDENCE.

23. JUST 7 YEARS LATER, ANOTHER BRIT NAMED ERNEST RUTHEFORD WAS DOING HIS OWN EXPERIMENTS. THESE TRIALS PRESENTED EVIDENCE THAT THE ATOM IS MOSTLY EMPTY SPACE, AND THE ELECTRONS ARE FAR, FAR AWAY FROM THE NUCLEUS.

24. Add this to your timeline: 1911 Atom is mostly empty space

25. MAKE AN INFERENCE… Why do you think we usually draw atoms like this When we know that the electrons are not that close to the nucleus?

26. IN 1913 IN HOLLAND, NIELS BOHR CONDUCTED EXPERIMENTS WITH EVIDENCE THAT THE ELECTRONS ORBIT THE NUCLEUS IN LAYERS, OR VALENCE SHELLS. HE OBSERVED THAT ATOMS GIVE OFF ENERGY WHEN ELECTRONS MOVE BETWEEN LAYERS.

27. BOHR‘S MODEL IS ALSO IN USE TODAY WHEN WE NEED TO PICTURE HOW THE ELECTRONS ARE ARRANGED.

28. Add this to your timeline: 1913 Electrons are arranged in shells

29. IN 1923 JAMES CHADWICK‘S EVIDENCE SHOWED THAT THERE WAS SOMETHING ELSE IN THE NUCLEUS BESIDES PROTONS, BUT THEY DIDN'T HAVE A CHARGE – THEY WERE NEUTRAL. HE NAMED THESE BLOBS NEUTRONS. WE HAD TO RE-WRITE ALL OF THE TEXTBOOKS AGAIN !

30. Add this to your timeline: 1923 Nucleus has protons and neutrons

31. Many scientists worked together to gather evidence that the electrons don't travel in definite ovals, they zing all over the place and they're moving so fast that they are just a blur, or a cloud. Heisenberg Schrodinger deBroglie

32. ELECTRONS MAKE A "CLOUD" AROUND THE NUCLEUS THAT HAS SEVERAL LAYERS. KINDA LIKE BEES BUZZING AROUND A HIVE. A BALLOON INSIDE A BALLOON INSIDE A BALLOON…

33. Add this to your timeline: 1930s Electrons buzz around nucleus in the “electron cloud”

34. SCIENTISTS‘ EXPERIMENTS HAVE ALSO PRODUCED EVIDENCE THAT PROTONS AND NEUTRONS HAVE EVEN TINIER PARTICLES INSIDE CALLED QUARKS, HELD TOGETHER BY GLUONS. BUT THIS IS ANOTHER STORY….

35. HAVE WE ACTUALLY SEEN AN ATOM? This movie was made by moving a single atom at a time inside a scanning-tunneling electron microscope.

36. Add this to your timeline: Today Quarks, gluons, neutrinos, dark matter, anti-matter…

37. AFTER ALL OF THIS TALK, HERE ARE THE BIG IDEAS: (WRITE THESE DOWN BELOW YOUR TIMELINE)

38. WE MAKE MODELS TO HELP US UNDERSTAND WHAT ATOMS LOOK LIKE. Even though we know the models are not perfect, they are still useful to help us create a “vision” of what atoms look like and how they work.

39. WE KEEP CHANGING THE MODEL OF THE ATOM AS NEW EVIDENCE IS PRESENTED. Each scientist contributed evidence gathered by conducting experiments.

40. THE END OR IS IT? DO YOU THINK WE WILL EVER HAVE A DIFFERENT MODEL OF THE ATOM?