2. Who was Democritus? How did Dalton describe atoms? Do Now: Take out HW and Stamp sheet Answer the following in your notes

3. Dalton’s model (1803) Thomson’s plum-pudding model (1897) Rutherford’s model (1909) Bohr’s model (1913) Charge-cloud model (present) Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 125 Greek model (400 B.C.) "In science, a wrong theory can be valuable and better than no theory at all." - Sir William L. Bragg

4. His atomic theory of matter contains four hypotheses: Elements are made of tiny particles called atoms. All atoms of a given element are identical. The atoms of a given element are different from those of any other element Atoms of one element can combine chemically with atoms of another element to form compounds. A given compound always has the same relative number and types of atoms. Atoms are indivisible in chemical processes. Atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

5. Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 58

6. Thompson’s 1897 Experiment Using a cathode ray tube, Thomson was able to deflect cathode rays with an electrical field. The rays bent towards the positive pole, indicating that they are negatively charged.

7. Thomson proposed that atoms consist of small, negative electrons embedded in a massive, positive sphere. The electrons were like raisins in a plum pudding, called the ‘plum pudding’ model of the atom. J.J. Thomson discovered the electron and knew that electrons could be emitted from matter (1897).

8. beam of alpha particles radioactive substance gold foil circular ZnS - coated fluorescent screen Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 120

9. Rutherford Model In 1911, Ernest Rutherford conducted his gold foil experiment which helped improve our understanding of atomic structure. In 1911, Ernest Rutherford conducted his gold foil experiment which helped improve our understanding of atomic structure. He directed a narrow beam of alpha particles at a very thin sheet of gold foil. He directed a narrow beam of alpha particles at a very thin sheet of gold foil. Alpha particles (  ) are He atoms that have been stripped of their electrons Alpha particles (  ) are He atoms that have been stripped of their electrons

11. Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 57 n +

12. What he expected…

13. Because he thought the mass was evenly distributed in the atom. - - - - -

14. What he got… richocheting alpha particles

15. Rutherford Model  According to Thomson’s model, the heavy, positive alpha particles should pass easily through the gold, with only a slight deflection  And mostly that’s how it happened.  However, they found 1 in every 8000 particles had actually been deflected back toward the source.

17. Rutherford Model  Rutherford suggested a new structural model of the atom.  He stated that all the positive charge and the mass is concentrated in a small core in the center of the atom, AKA nucleus  And that the atom is mostly empty space with electrons surrounding the positively charged nucleus like planets around the sun.

18.  Take a minute and draw out what Rutherford thought that the atom looked like. (Don’t forget about the charge) Proton + ++++++ Electrons

19. Two atoms are walking down the street. One atom says to the other, “Hey! I think I lost an electron!” The other says, “Are you sure?” “Yes, I’m positive!” A neutron walks into a restaurant and orders a couple of drinks. As she is about to leave, she asks the waiter how much she owes. The waiter replies, “For you, No Charge!!!”

20.  Atoms are incredibly tiny.  Measured in picometers (10 -12 meters)  Hydrogen atom, 32 pm radius  Nucleus tiny compared to atom  Radius of the nucleus near 10 -15 m.  Density near 10 14 g/cm 3  IF the atom was the size of a stadium, the nucleus would be the size of a marble. California WEB

21.  7Km and 27 km

23. electron e-e-e-e-0 Outside of nucleus proton p+p+p+p++11 Inside nucleus neutron n0n0n0n001 Structure of the Atom

24. There are two regions 1. Nucleus  Contains protons and neutrons  Has a positive charge  Almost all the mass 2. Electron Cloud  Where electrons are found  Has a negative charge  Almost all the volume Single Atom Water Molecule