The Atom

1. The Atom Chapter 4 http://www.youtube.com/watch?v=Uy0m7jnyv6U

2. History of the Atomic Theory A. Democritus B. Aristotle C. Lavoisier D. Proust E. Dalton F. Modern Atomic Theory • History of Atomic Structure A. Thomson B. Milikan C. Rutherford D. Bohr E. Chadwick F. Quantum Atom • Subatomic Particles A. Atomic Number B. Mass Number and Isotopes C. Electrons and Ions D. Nuclear and Hyphenation Notation E. Average Atomic Mass • Weighing and Counting Atoms A. Mole Atoms B. Mole Mass C. Mass Atoms

3. I. History of the Atomic Theory • Remember: a scientific theory explains behaviors and the ‘nature’ of things • Theories can be revised when new discoveries are made • The theory describing the composition of matter has been revised many times

4. I. History of the Atomic Theory • Democritus (460-370 BC) 1.Matter is made up of “atoms” that are solid, indivisible and indestructible 2.Atoms constantly move in space 3.Different atoms have different size and shape 4.Changes in matter result from changes in the grouping of atoms 5. Properties of matter result from size, shape and movement

5. I. History of the Atomic Theory B. Aristotle(384-322 BC ) & Others 1. Four kinds of matter a. Fire – Earth – Water – Air 2. One kind of matter can transform into another 3. Rejected idea of the “atom” (idea then ignored for almost 2000 years 4. This theory was more popular and it was easier to accept

6. Aristotle’s Theory of Matter

7. I. History of the Atomic Theory • Antoine Lavoisier (1770s) 1. Experiment: 2 Sn + O2 2 SnO tin oxygen tin (II) oxide mass before reaction = mass after reaction 2. Law of Conservation of Mass a. Matter cannot be created or destroyed (in a chemical or physical change)

9. I. History of the Atomic Theory • Joseph Proust (1779) 1. Develops Law of Definite Composition- all samples of a specific substance contain the same mass ratio of the same elements a. ex: all samples of CO2 contains 27.3% carbon and 72.7% oxygen b. therefore ‘elements’ are combining in a whole number ratio – WHY????

10. I. History of the Atomic Theory - Dalton • John Dalton (1803) 1. Develops Law of Multiple Proportions a. describes the ratio of elements by mass in two different compounds composed of the same elements 2. Example: carbon monoxide carbon dioxide 1 part oxygen : 2 parts oxygen *when compared to the same amount of carbon in each compound

11. I. History of the Atomic Theory- Dalton 3. Dalton collects data and develops his atomic theory in 1803

12. 4. Dalton’s Background • Dalton became a school teacher at the age of 12 (he left school at age 11) • loved meteorology - pioneer in this field • studied works of Democritus, Boyle and Proust • Wrote New System of ChemicalPhilosophy in 1808

13. 5. Dalton’s Atomic Theory 1. Matter is made of small particles-atoms 2. Atoms of a given element are identical in size, mass, but differ from those of other elements*. 3. Atoms cannot be subdivided or destroyed*. ( supports law of conservation of mass) 4.Atoms combine in small whole number ratios to form compounds. (def comp,Mult prop) 5. Atoms combine, separate, or rearrange in chemical reactions. * Modified in Modern Atomic Theory

14. JUST A THEORY……. • But it lead to the • Modern Atomic theory

15. F. Modern Atomic Theory • All matter is made up of small particles called atoms. • Atoms of the same element have the same chemical properties while atoms of different elements have different properties • Not all atoms of an element have the same mass, but they all have a definite average mass which is characteristic. (isotopes)

16. F. Modern Atomic Theory • Atoms of different elements combine to form compounds and each element in the compound loses its characteristic properties. • Atoms cannot be subdivided by chemical or physical changes – only by nuclear changes

17. I. History of the Atomic Theory

18. History of the Atomic StructureA. J.J. Thomson (1856-1940) J.J. Thomson (1887) • Experiments with cathode ray tubes a. atoms have (-) charged particles which are smaller than atoms b. determined charge/mass ratio of the “electron”

19. Voltage source - + Vacuum tube Metal Disks

20. Voltage source - +

21. Voltage source - +

22. Voltage source - +

23. Voltage source - + • Passing an electric current makes a beam appear to move from the negative to the positive end

24. Voltage source - + • Passing an electric current makes a beam appear to move from the negative to the positive end

25. Voltage source - + • Passing an electric current makes a beam appear to move from the negative to the positive end

26. Voltage source - + • Passing an electric current makes a beam appear to move from the negative to the positive end

27. Voltage source • By adding an electric field

28. Voltage source + - • By adding an electric field

29. Voltage source + - • By adding an electric field

30. Voltage source + - • By adding an electric field

31. Voltage source + - • By adding an electric field

32. Voltage source + - • By adding an electric field

33. Voltage source + - • By adding an electric field he found that the moving pieces were negative

34. Demonstration of the cathode ray experiment.

35. Thomson’s Model The Pudding Model • a. electrons present • b. atom is like plum pudding - bunch of positive stuff (pudding), with the electrons suspended (plums)

36. History of the Atomic StructureB. Robert Milikan (1868-1953) 1. Oil Drop Experiment (1909) a. Discovered mass and actual charge of electron (-1) b. Mass is 1/1840 the mass of a hydrogen atom 1) e – has a mass of 9.11 x 10-28 g

37. Oil Drop

38. History of the Atomic Structure – Summary thus far • So, at this point we know: - Atoms are divisible into smaller particles • Electrons are negatively charged • The mass of an electron is very small HOWEVER • Atoms should have a (+) portion to balance the negative part - Electrons are so small that some other particles must account for mass

39. II. History of the Atomic StructureErnest Rutherford (1871-1937) C.Ernest Rutherford (1909) 1. Discovered the proton p+ 2. Received Nobel Prize in Chemistry 3. Gold Foil Experiment (Expectations) a. Shot alpha particles at atoms of gold b. expected them to pass straight through

40. Florescent Screen Lead block Uranium Gold Foil

41. He thought this would happen:

42. According to Thomson Model

43. He thought the mass of the positive charge was evenly distributed in the atom

45. Here is what he observed:

46. 4. Gold Foil Experiment Results a. Most positive alpha particles pass right through b. However, a few were deflected c. Rutherford reasoned that the positive alpha particle was deflected or repelled by a concentration of positive charge

47. The positive region accounts for deflection

48. 5. Gold Foil Experiment Conclusions a. the atom is mostly empty space b. the atom has a small, dense positive center surrounded by electrons Rutherford Model of the Atom

49. II. History of the Atomic Structure • At this point in 1909, we know: • p+ = 1.67 x 10-24 g • e- = 9.11 x 10-28 g • The charges are balance! • But, • How are the electrons arranged? • There is still mass that is unaccounted for

50. II. History of the Atomic Structure • Niels Bohr (1913) 1. Electrons orbit nucleus in predictable paths