Evolution of Atomic Theory: Dalton's Legacy & Modern Insights

1. Chapter 3 Atoms

2. law of conservation of mass law of definite proportions law of multiple proportions Vocabulary

3. Objectives Explainthe law of conservation of mass, the law of definite proportions, and the law of multiple proportions. Summarizethe five essential points of Dalton’s atomic theory. Explainthe relationship between Dalton’s atomic theory and the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. Ch. 3 Section 1 The Atom: From Philosophical Idea to Scientific Theory

4. Section 3.1 Defining the Atom Around 460 B.C. Greek philosopher, Democritus, developed the idea of atoms. He asked this question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further? Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms.

5. Democritus’s Atomic Philosophy • Atom comes from the • Greek word atomos, meaning “indivisible” • His ideas: • were based on philosophy • didn’t explain chemical behavior • lacked experimental support • Atoms wereindivisible andindestructible

6. A. Three Atomic Laws • Rules that explain how matter interacts in chemical reactions: 1790’s- improved balances revolutionized quantitative analysis of chemical reactions.. allowed accurate measure of masses of elements and compounds Law of conservation of mass mass is neither created nor destroyed during ordinary chemical reactions or physical changes

7. A. Three Atomic Laws • Rules that explain how matter interacts in chemical reactions: 2. Law of definite proportions a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source 3. Law of multiple proportions two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

8. Chapter 3 Section 1 The Atom: From Philosophical Idea to Scientific Theory Law of Conservation of Mass

9. Section 1 The Atom: From Philosophical Idea to Scientific Theory Chapter 3 Law of Multiple Proportions

10. John Dalton (1766-1844) • Developed an atomic theorybased on results of experiments Note: Dalton was always very smart and at the age of twelve he took over a Quaker school in Cumberland, England. Designated much of his life to researching color blindness because both he and his brother suffered from it. Dalton transformed Democritus’s ideas on atoms into a scientific theory. Dalton used experimental methods not just philosophy Studied ratio in which elements combine in chemical reactions

11. Dalton’s Elements and Compounds

12. B. Dalton’s Atomic Theory (p. 64) All elements are composed of extremely small particles called atoms. Atoms of an element are identical in size, mass and other properties; atoms of different elements differ in size, mass, and other properties.

13. B. Dalton’s Atomic Theory (p. 64) (law of conservation of mass) (law of definite proportions and multiple proportions) (law of conservation of mass) 3. Atoms cannot be subdivided, created, or destroyed 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged.

14. Scanning Tunneling Microscope (STM) Gerd Binnig Dr. Heinrich Rohrer • Invented in 1981 by Gerd Binnig and Heinrich Rohrer working for IBM in Zurich, Switzerland. • Won 1986 Nobel Prize in physics for their discovery • Opened door to field of Nanotechnology Scanning Tunneling Microscopy

15. Use of Scanning Tunneling Microscopy by IBM Moving Atoms: Making the World's Smallest Movie The Boy and His Atom

16. Scanning Tunneling Microscope (STM) • STM provides ability to look at individual atoms • detects the electrons of surface atoms • maps the position and spacing of atoms

17. Modern Atomic Theory Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that: • Atoms are divisible into even smaller particles. • A given element can have atoms with different masses (isotopes). Some important concepts remain unchanged: • All matter is composed of atoms. • Atoms of any one element differ in properties from atoms of another element. Dalton’s Atomic Theory has not been discarded.. only modified!

18. Chapter 3 Atoms

19. atom nuclear force Vocabulary

20. Objectives Summarizethe observed properties of cathode rays that led to the discovery of the electron. Summarizethe experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. Listthe properties of protons, neutrons, and electrons. Defineatom. Describenuclear forces Chapter 3 Section 2 The Structure of the Atom

21. Section 3.2 Structure of the Atom Electrons, protons, and neutrons One change to Dalton’s atomic theory - atoms ARE divisible Into subatomic particles:

22. Thomson’s Cathode-Ray Tube Experiment

23. Discovery of Electron- J.J. Thomson p. 69 1897 - J.J. Thomsonusedcathode ray tubeto show presence of negatively charged particles...electrons Note: Called the negatively charged particles “corpuscles” JJ Thomson's Cathode-Ray Tube Experiment

24. Thomson’s Atomic Model J. J. Thomson • cathode ray experiment showed presence of electrons • “plum pudding” model - believed e- like plums in + charged “pudding,” • charge-to-mass ratio of an electron

25. Joseph John “J.J.” Thomson1856-1940 Famous for discovery of the first subatomic particle, the electron, and for work on the atomic model. It was soon superseded by his student Ernest Rutherford’s nuclear model. 1906 received Nobel Prize for physics for his research into the electrical conductivity of gases. Thomson was a great teacher and an outstanding scientist. Seven of his students and assistants also received Nobel Prizes for their work.

26. CRT - Cathode Ray Tube Television Computer Monitor Cathode ray tube (CRT) is a vacuum tube containing an electron gun (source of electrons) and fluorescent screen used to view images. It accelerates and deflects the electron beam onto fluorescent screen to create images. Can be found in everyday devises such as televisions, video games, computers, video cameras, monitors, automated teller machines, oscilloscopes, and radar displays. CRTs have been superseded by more modern display technologies such as LCD, plasma display, andOLED, which as of 2012 offer lower manufacturing and distribution costs.

27. Millikan’s Oil Drop Experiment Robert Millikan Starting in 1908, while a professor at the University of Chicago, Millikan worked on an oil-drop experiment in which he measured the charge on a single electron. J.J. Thomason had already discovered the charge-to-mass ratio of the electron. However, the actual charge and mass values were unknown. Therefore, if one of these two values were to be discovered, the other could easily be calculated. Millikan and his then graduate student Harvey Fletcher used the oil-drop experiment to measure the charge of the electron (as well as the electron mass, and Avogadro’s number, since their relation to the electron charge was known). Millikan showed that the results could be explained as integer multiples of a common value (1.592 × 10−19 coulomb), the charge on a single electron. That this is somewhat lower than the modern value of 1.602 176 53(14) x 10−19 coulomb is probably due to Millikan's use of an inaccurate value for the viscosity of air.

28. Charge and Mass of Electron- Robert Millikan Charge of the electron is 1.592 × 10−19 coulomb The oil drop apparatus • determined the actual e- charge: 1.592 × 10−19 coulomb) (Somewhat lower than the modern of 1.602 × 10 −19 coulomb) • determined actual e- mass: 1/1837 the mass of H atom (9.11 x 10-28 g) Robert Millikan's Oil drop experiment

29. Robert Millikan (1868-1953) • Doctorate in Physics from Columbia University • 1923 Nobel Prize for Physics • Determined charge on the electron as well as Planck’s constant Millikan set up his experiment by spraying oil drops, which fell between positively charged plate and negatively charged plate. He balanced the electric charge with electron's weight, as gravity pulled down on the oil drop, and the electric charges attracted and repelled it. Using this method, he discovered that the charge of an electron is negative. The weight of each drop was determined by observing it's rate of free fall through the air. Originally, he sprayed droplets of water through an electrical field that was intended to suspend them in midair, but the water droplets evaporated too fast, so Millikan switched to using oil.

30. Conclusions from Electron study: • Because atoms are electrically neutral, they must contain a positive charge to balance the negative e- • Because electrons have so much less mass than atoms, atoms must contain other particles that account for most of their mass.

31. Discovery of Protons: Eugen Goldstein • 1886 -Eugen Goldsteinobserved + particles (now called “proton”) • particles with +charge & relative mass of 1 (or 1840x e-) • called them “Canal rays” (anode rays)

32. Eugen Goldstein (1850-1930) Credited by many for the discovery of the existence of protons discoverer of anode rays (canal rays) Worked in Berlin and Potsdam Observatories

33. Rutherford’s Gold Foil Experiment

34. Ernest Rutherford’s1911- Gold Foil Experiment • Alpha particles fired at gold foil • Particles hitting detecting screen were recorded

35. Discovery of Nucleus: Ernest Rutherford “It was as if you fired a 15-in [artillery] shell at a piece of tissue paper and it came back and hit you.” • most particles passed thru • few deflected • VERY FEW greatly deflected Conclusions: • small, dense nucleus • + charged nucleus

36. Rutherford’s Atomic Model Rutherford’s Atom 3:08 Experimental evidence: • atom mostly empty space • almost all mass innucleus • e- distributed around nucleus…occupy most of the volume • called “nuclear model”

37. Discovery of Neutrons: James Chadwick 1932 –James Chadwick confirmed existence of the “neutron” • particle with no charge • n0 mass = p+ mass 1935 - Nobel Prize for Physics Prepared the way for the fission of Uranium-235 which led to developing atomic bomb (Manhattan Project)

38. C. Atomic Scientists • Democritus • John Dalton • J.J. Thomson • Robert A. Millikan • With this information, scientists were able to determine the mass of an electron. named the atom proposed the Atomic Theory cathode-ray tube experiments measured the charge-to-mass ratio of an electron. (plum-pudding model) oil drop experiment measured the charge of an electron

39. C. Atomic Scientists • Rutherford: • James Chadwick: gold foil experiment Discovered small, dense nucleus Positive charged nucleus proved existence of neutrons.. no charge

40. D. Subatomic Particles Outside Nucleus (Electron cloud) 0 1- 9.11 x 10-28 Nucleus 1.67 x 10-24 1 1+ Nucleus 1.67 x 10-24 1 0

41. The Structure of the Atom Anis the smallest particle of an element that retains the chemical properties of that element. Chapter 3 Section 2 The Structure of the Atom atom • The is a very small region located at the center of an atom. nucleus • The nucleus is made up of at least one positively charged particle called a and usually one or more neutral particles called . proton neutrons

42. The Structure of the Atom Surrounding the nucleus is a region occupied by negatively charged particles called . Protons, neutrons, and electrons are often referred to as . Chapter 3 Section 2 The Structure of the Atom electrons subatomic particles

43. The Structure of the Atom Atoms are electrically because they contain equal numbers of protons and electrons The nuclei of atoms of different elements differ in their number of and therefore in the amount of positive charge they possess. Thus, the number of determines that atom’s identity. Chapter 3 Section 2 The Structure of the Atom neutral protons protons

44. Properties of Subatomic Particles Chapter 3 Section 2 The Structure of the Atom

45. Forces in the Nucleus Chapter 3 Section 2 The Structure of the Atom When two protons are extremely close to each other, there is a strong attraction between them. A similar attraction exists when neutrons are very close to each other or when protons and neutrons are very close together. The short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together are referred to as nuclear forces.

46. Chapter 3 Section 2 The Structure of the Atom The Sizes of Atoms • The radius of an atom is the distance from the center of the nucleus to the outer portion of its electron cloud. • Because atomic radii are so small, they are expressed using a unit that is more convenient for the sizes of atoms. • This unit is the picometer, pm.

47. atomic number isotope mass number nuclide unified atomic mass unit average atomic mass mole Avogadro’s number molar mass Vocabulary

48. Chapter 3 Section 3 Counting Atoms Objectives • Explain what isotopes are. • Defineatomic number and mass number, and describe how they apply to isotopes. • Given the identity of a nuclide, determine its number of protons, neutrons, and electrons. • Definemole, Avogadro’s number, and molar mass, and state how all three are related. • Solveproblems involving mass in grams, amount in moles, and number of atoms of an element.

49. Atomic Number • Atoms of different elements have different numbers of • Atoms of the same element all have the same number of • The (Z) of an element is the number of protons of each atom of that element. protons protons. atomic number

50. Atomic Number = number of protons