2. Warm Up Work silently. Raise hand to ask Ms. Hughes anything. 1.Why must scientists repeat the experiments of other scientists? 2.True or false: scientific theories are only good if they never change over time

3. Take 1

4. Announcements Unit 8A test this Thursday (4/1) Keep on top of your work/grades…make up or retake units 6 + 7!!!

5. In chemistry, energy is stored in chemical bonds

6. The main form of energy in chemistry is HEAT!

7. Why does the temperature change?!? Key Point #1: Breaking a bond requires energy. Forming new bonds releases energy. Unit for energy: kilojoules (kJ)

8. Endothermic Reactions Key Point #2: If the total heat taken in by a reaction is more than the heat released, it is called an endothermic reaction. REACTANTS PRODUCTS Net energy is absorbed!

9. Endothermic = energy ABSORBED energy goes IN

10. Exothermic Reactions Key Point #3: If the total heat released by a reaction is more than the heat taken in, it is called an exothermic reaction. REACTANTS PRODUCTS Net energy is released!

11. Exothermic = energy RELEASED energy EXITS

12. Endo or Exo??? 1. 2 HCl + 185 kJ  H 2 + Cl 2 2. 4 NH 3 + 5 O 2  4 NO + 6 H 2 O + 1169 kJ 3. Cu + Cl 2  CuCl 2 + 220.1 kJ 4. H 2 O + C + 132 kJ  CO 2 + 2H 2

13. Some Questions to ponder The combustion of the hydrocarbon glucose (C 6 H 12 O 6 ) produces carbon dioxide, water, and releases 2830 kJ. Exo or Endo???

14. Some Questions to ponder After absorbing 66.4 kJ of energy, 1 mole of nitrogen gas and 2 moles of oxygen gas react to form 2 moles of nitrogen monoxide. Exo or Endo???

15. Practice- Energy worksheet

16. More balancing chemical equations practice!!!

17. Big Players in Atomic Theory Democritus (460-370 B.C.) Aristotle (384-322 B.C.) John Dalton (1808) J.J. Thomson (1898) R.A. Millikan (1909) Ernest Rutherford (1909) Niels Bohr (1913) Chadwick (1932) Schrodinger (1936)

18. Democritus - Conclusions Matter is composed of tiny INDIVISIBLE (can’t be broken down) particles Different kinds of particles have different sizes and shapes Particles move through empty space Page 88

19. 1)Democritus 420 B.C, Greece - Matter is made of “tiny, indivisible particles”, called atoms and empty space. No experiments. REJECTED!

20. Coming in Third… John Dalton (1766-1844) Experiment: Careful chemical measurements Where: England When: 1803 Page 90

21. Four Postulates All matter is made of tiny particles called atoms. All atoms of a given element are identical, but they differ from those of any other element.

22. Four Postulates Compounds are formed by a combination of 2 or more types of atoms. Chemical reactions occur when atoms are rearranged.

23. What were Dalton’s conclusions? Atoms are hard, round, solid balls. They are similar to marbles.

24. Cuatro! J. J. Thomson (1856-1940) Experiment: Cathode ray tube When: 1898 Where: England

25. Thomson’s Cathode Ray Tube Electrons are NEGATIVE!

26. Thomson’s Cathode Ray Tube Quick! Reading Time! Pages 92-93 Stop at “The next significant development….”

27. He said the atom is a ball with electrons floating around in a sea of positive space Atoms can be divided into smaller SUBATOMIC particles! Thomson’s CONCLUSIONS

28. Thomson’s Conclusions Now I can finish my model! It looks like Plum Pudding! Or like a chocolate chip cookie!

29. Numero Cinco! - R. A. Millikan Experiment: Millikan Oil Drop Experiment When: 1909 Where: U.S.A!!!!

30. Millikan’s Oil Drop Experiment

31. Millikan! Sprayed oil drops Drops fell between magnetic plates Drops radiated to give them negative charge Measured how fast they fell to find charge and mass Gravity pulls them down…But since opposite charges attract and likes repel The magnetic plates pushed the drops up

32. Millikan’s Calculations – Whoa!

33. What were Millikan’s conclusions? I have most accurately measured the charge of an electron: -1.59 x 10 -19 Coulombs

34. What were Millikan’s conclusions? I have also most accurately measured the mass of an electron: 9.109 x 10 -31 kg

35. What were Millikan’s conclusions? The electron is really really small and has a negative charge

36. Numero Seis! - Ernest Rutherford Experiment: Gold Foil Experiment When: 1910 Where: Montreal

37. Gold Foil Experiment Explained Alpha helium particles were shot through a piece of gold foil –Think aluminum foil but thinner and made out of gold! Alpha helium particles are 8000 times more massive (bigger) than electrons Rutherford thought alpha particles would knock electrons out of the way, since atom is only electrons in sea of positive charge

38. http://micro.magnet.fsu.edu/electromag/java/rutherford/

39. Remember! This is the current model of the atom (Thanks to Thomson)

40. More History Ernie’s (Rutherford) Big Adventure Thin Sheet of Gold Atoms

41. - - -- +

42. What were Rutherford’s conclusions? Discovered the nucleus, a concentrated mass with positive protons! Nucleus is in the center of the atom The atom is mostly empty space Electrons orbit around nucleus

43. What’s this empty space idea? The atom is mostly empty space! The nucleus is TINY compared to the size of the entire atom! Called “the planetary model” because electrons orbit like planets in empty space

44. Relative Size of Nucleus to the Atom

45. James Chadwick Experiment: Beryllium Foil Experiment When: 1932 Where: Cambridge (England)

46. Beryllium foil experiment Similar to gold foil experiment Shot alpha particles at beryllium foil Noticed neutral radiation coming out That neutral radiation could knock protons out of the way Therefore, heavy neutral particles exist in the atom

47. What were Chadwick’s conclusions? Neutral radiation emitted; therefore, the nucleus contains another subatomic particle called the neutron (has a neutral charge)

48. - - -- ++ + + - - - - NUCLEUS NEUTRON ELECTRON PROTON

49. Theories are Supported or not supported by evidence Example: Rutherford’s gold foil experiment did NOT support the plum pudding model

50. New scientific data Can cause scientific theories to change

51. Experimental results must be REPRODUCIBLE to be valid

52. Remastery quiz Work silently and alone to receive full credit

53. Last minutes What did we learn today? Top ten: how’d we do?