History and Science of Atomic Theory

1. Catalyst – February 20-1, 2013HW/Vocab Out! • Fill in the blanks using the word bank below. • Disproven, revise, theory, accept, stronger • In science, a _(1)__ is an attempt to explain a particular aspect of the universe. Theories can't be proven, but they can be __(2)__. If observations and tests support a theory, it becomes __(3)__ and usually more scientists will __(4)__it. If the evidence contradicts the theory, scientists must either discard the theory or __(5)__it in light of the new evidence.

2. Today’s Agenda • Catalyst • Surprise • Atomic Theory Day!! • Videos, Notes, Thinking, Simulations, etc! • Progress Reports and Lab Fees • No Exit Question Today HW: Workbook pages 47-48 Honors HW: Workbook pages 47-49

3. Today’s Objectives • SWBAT trace the evolution of atomic theory from 420 B.C. to the present using word descriptions and models. • SWBAT identify scientific discoveries that led to new models and more understanding of the atom.

4. Surprise! Pop Quiz! Must be SILENT! • You may use your HOMEWORK AND VOCAB LIST!

5. Meet your new BEST FRIENDS!!!!

6. LESSON TITLE: HISTORY AND SCIENCE OF ATOMIC THEORY

7. Acceptance of Scientific DiscoveryThe Long Version • Use the following rules of evidence to examine experimental results: • Can an expert's technique or theory be tested, has it been tested, or is it simply a subjective, conclusive approach that cannot be reasonably assessed for reliability? • Has the technique or theory been subjected to peer review and publication? • What is the known or potential rate of error of the technique or theory when applied? • Were standards and controls applied and maintained? • Has the technique or theory been generally accepted in the scientific community?

8. Acceptance of Scientific Discovery“Cliff’s Notes” • Use the following rules of evidence to examine experimental results: • Has it been adequately tested? • Has peer review occurred? • What kind of error does it have? • Were there standards or control groups? • Has it been accepted by scientific community?

9. What is an atom? Atom: the smallest particle of an element that retains (keeps) its identity in a chemical reaction

10. Major Playas of Atomic Theory Democritus (460-370 B.C.) John Dalton (1808) J.J. Thomson (1897) Ernest Rutherford (1909) Niels Bohr (1913) Schrodinger (1926) [James Chadwick (1932)]

11. Acceptance of Scientific Discovery“Cliff’s Notes” • Use the following rules of evidence to examine experimental results: • Has it been adequately tested? • Has peer review occurred? • What kind of error does it have? • Were there standards or control groups? • Has it been accepted by scientific community?

12. FIGHTING SCIENTISTS!

13. VIDEO!

14. Democritus (460-370 B.C.) • Where: Greece • When: 420 B.C. • Experiment: Observations and inferences • No REAL experiment…just IDEAS • First “theory” of the atom MODEL 

15. FIGHTING SCIENTISTS!

16. What were Democritus’ conclusions? • Matter is composed of tiny particles called atomos • Different kinds of particles have different sizes and shapes • Atoms are indivisible and indestructible

17. BACK TO VIDEO!

18. John Dalton (1766-1844) • Where: England • When: 1808 • Experiment: Many careful chemical measurements and experiments!

19. Dalton’s Postulates (in textbook) • In 1808, John Dalton came up with the first atomic theory that was based on scientific research. • It stated: • All matter is made of atoms. • Atoms are indivisible and indestructible. • All atoms of a given element are identical in mass and properties • Compounds are formed by a combination of two or more different kinds of atoms. • A chemical reaction is a rearrangement of atoms.

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

21. WHAT’S IN THE BOX??

22. J. J. Thomson (1856-1940) • Where: England • When: 1897 • Experiment: Cathode ray tube

23. BACK TO VIDEO!

24. Thomson Model Where did they come from? • This surprised Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from?

25. Thomson’s Cathode Ray Experiment • Passed electric current through gases at low pressure • As the current passed through the gas, it was attracted to a positively charged plate outside of the tube

26. Thomson’s Cathode Ray Experiment -- +

27. Thomson concluded that the negative charges came from ________the atom. A particle _________ than an atom had to exist. The atom was _________! within smaller divisible Thomson called the negatively charged “corpuscles,” today known as ____________. Since the gas was known to be neutral, having no charge, he reasoned that there must also be __________ charged particles in the atom. But he could never find them…. electrons positively

28. What were Thomson’s conclusions? • Electrons have a very, very small mass; therefore, they must be smaller than atoms • Atoms have parts of them that are negatively charged • Credited with discovering the electron

29. Thomson was pretty hungry when… Now I have finished my model! It looks like Plum Pudding! MODEL 

30. Ernest Rutherford • Where: England (University of Manchester) • When: 1909 • Experiment: Gold Foil Experiment

31. Lil’ Ernie Rutherford on the Scene! Rutherford shot positively charged alpha particles at a very thin piece of gold foil

32. What Lil’ Ernie thought would happen… If the Plum Pudding model was true, all of the positively charged alpha particles would have gone straight through the foil

33. What Actually Happened… ? • Almost all of the alpha particles went straight through, but some were deflected • 1 in 8000 of the alpha particles was deflected

34. Simulation http://phet.colorado.edu/simulations/sims.php?sim=Rutherford_Scattering

36. What do you think? • Pretend you are Rutherford • As Rutherford, what conclusion would you make based on the data from the Gold Foil Experiment? Hint: Positive repels positive, negative repels negative =

37. Rutherford’s Conclusions • The atom is mostly empty space through which negatively charged electrons move • There is a tiny, dense region in the center of the atom called the nucleus (positively charged)

38. - - - - +

39. MODEL 

40. Relative Size of the Nucleus to the Atom

41. Still Some Unanswered Questions • Rutherford’s model of the atom did not explain HOW the atom’s electrons are arranged in the space around the nucleus • Nor did it address the question of WHY the negatively charged electrons are not pulled into the atom’s positively charged nucleus

42. 1900s…Chemical Behavior • Scientists observed that certain elements emitted visible light when heated in a flame • Analysis of the emitted light revealed that and element’s chemical behavior is related to the arrangement of electrons in atoms

43. Niels Bohr • Where: England (at Rutherford’s lab) • When: 1913 • Experiment: Atomic emission spectra

44. The Next Great Idea • Niels Bohr studied the atomic emission spectrum for the simplest atom, hydrogen • Each orbit has its own fixed energy = energy level • With the right amount of energy, electrons can move from one energy level to another, but they cannot exist between energy levels

45. Atomic Emission Spectra

46. NOT BOHR-ING AT ALL!!!

47. Bohr’s Conclusions • Electrons orbit around the nucleus in distinct circular paths called energy levels!

48. Erwin Schrodinger Where: Austria When: 1926 Experiment: Furthered other scientists’ work

49. Wave Model…aka… Quantum Mechanical Model

50. The Wave Model • In fact, it is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has. • Today’s atomic model is based on the principles of wavemechanics. • According to the theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun.