2. Atoms and their structure

3. Labs n Labs are now online is a Google Docs folder n You can view the lab if you lose it (and you can copy and paste the procedure – so stop whining about having to rewrite it) n You can submit your Labs via Google Docs by sharing them with me (cconciatori@valhallaschools.org) cconciatori@valhallaschools.org

4. Another Greek n Aristotle - Famous philosopher n All substances are made of 4 elements –Fire - Hot –Air - light –Earth - cool, heavy –Water - wet n If you blend these in different proportions you can get all substances

5. Who ’ s Next? Late 1700’s - John Dalton- England. Late 1700’s - John Dalton- England. Elements are substances that can’t be broken down Elements are substances that can’t be broken down

6. Dalton ’ s Atomic Theory  All matter is made of tiny indivisible particles called atoms.  Atoms of the same element are identical, those of different atoms are different.  Atoms of different elements combine in whole number ratios to form compounds.  Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.

7. Law of Definite Proportions n Each compound has a specific ratio of elements. n It is a ratio by mass. n Water is always 8 grams of oxygen for each gram of hydrogen.

8. Parts of Atoms n J. J. Thomson - English physicist. 1897 n Made a piece of equipment called a cathode ray tube. –It is a vacuum tube - all the air has been pumped out. –A limited amount of other gases are put in

9. Thomson ’ s Experiment Voltage source +- Metal Disks

10. After connecting a battery to the tube, a beam appeared start at the negative end and move to the positive end Thomson ’ s Experiment Voltage source +-

11. Thomson ’ s Experiment He created an electrical charge around the tube and the beam always bent towards the positive + -

12. Voltage source Thomson ’ s Experiment He determined the beam was made of negative particles + -

13. Thomson ’ s Experiment n Used many different metals and gases n The beam was always the same n By the amount it bent he could find the ratio of charge to mass n It was the same with every material

14. Thompson ’ s Model n Found the electron. Couldn’t find positive particle(for a while). Couldn’t find positive particle(for a while). n Said the atom was like plum pudding. n A bunch of positive stuff, with the electrons able to be removed.

15. Millikan ’ s Experiment Atomizer Microscope - + Oil Metal Plates

16. Millikan ’ s Experiment Oil Atomizer Microscope - + Oil droplets

17. Millikan ’ s Experiment X-rays X-rays give some drops a charge by knocking off electrons

18. - Millikan ’ s Experiment +

19. They put an electric charge on the plates + + --

20. Millikan ’ s Experiment Some drops would hover + + --

21. Millikan ’ s Experiment + ++ +++++ -- ----- Some drops would hover

22. Millikan ’ s Experiment From the mass of the drop and the charge on the plates, he calculated the charge on an electron + + --

23. Rutherford ’ s Experiment n Ernest Rutherford English physicist. (1910) n Believed the plum pudding model of the atom was correct. n Wanted to see how big atom are n Shot alpha particles at gold foil which can be made a few atoms thick. n Alpha particles - positively charged particles.

24. Rutherford ’ s experiment n When the alpha particles hit a florescent screen, it glows.

25. Lead block Uranium Gold Foil Flourescent Screen

26. He Expected n The alpha particles to pass through without changing direction very much.

27. What he expected

28. What he got

29. How he explained it + n Atom is mostly empty space. n Small dense, positive piece at center. n Alpha particles are deflected by it if they get close enough. (like charges repel)

30. +

31. Bohr Model n Planetary model n Electrons in definite fixed orbits n How we currently draw atoms

32. Wave-Mechanical Model n Most modern model of the atom n Gives electrons properties of both particle and wave n Electrons with distinct amounts of energy moving in orbitals n Orbitals = region in which electron is likely to be located

33. Modern View n The atom is mostly empty space. n Two regions. n Nucleus- protons and neutrons. n Electron cloud- region where you might find an electron.