The Greeks History of the Atom

1. ~ ~ The GreeksHistory of the Atom • Not the history of atom, but the idea of the atom • In 400 B.C the Greeks tried to understand matter (chemicals) and broke them down into earth, wind, fire, and air. (continuous matter) • Greek philosophers (Aristotle, Democritus, others)

2. Carbon dioxide, CO2 Methane, CH4 Water, H2O Daltons’ Model of the Atom

3. Dalton’s Atomic Theory (1803) 1. All matter is made of tiny indivisible particles called atoms. 2. Atoms of the same element are identical, those of different atoms are different. 3. Atoms of different elements combine in whole number ratios to form compounds 4. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed. California WEB

4. Foundations of Dalton’s Atomic Theory • Law of Conservation of Mass • Mass is neither destroyed nor created during ordinary chemical reactions (Lavoisier). • Law of Definite Proportions • The fact that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound (Proust). • Law of Multiple Proportions • If 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 elements is always a ratio of small whole numbers (Dalton).

5. Thomson’s (J.J.) Discovery of the Electron J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube (all the air has been pumped out) with fluorescent screen. Experiments led to the discovery of the electron.

6. Thomson’s Experiment voltage source - + vacuum tube metal disks

7. Thomson’s Experiment voltage source ON - OFF + Passing an electric current makes a beam appear to move from the negative to the positive end

8. + - Thomson’s Experiment voltage source ON - OFF + By adding an electric or magnetic field… he found that the moving pieces were negative.

9. Spherical cloud of Positive charge Electrons Thomson’s Model of the Atom • In 1897 proposed the Plum Pudding model • Negative electrons were embedded into a positively charged spherical cloud. Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 56

10. Rutherford’s Model of the Atom • Learned physics in J.J. Thomson’ lab. • Noticed that ‘alpha’ particles were sometime deflected by something in the air. • Gold-foil experiment led to rejection of plum pudding model (1909)

11. Rutherford’s Scattering (1909) Rutherford received the 1908 Nobel Prize in Chemistry for his pioneering work in nuclear chemistry. beam of alpha particles radioactive substance circular ZnS - coated fluorescent screen gold foil Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120

12. What he expected… California WEB

13. What he got…

14. . . . . . . . . . . . . . . gold foil Interpreting the Observed Deflections . beam of alpha particles undeflected particles . . deflected particle Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120

15. Rutherford’s Conclusions • Since most of the particles went through, the atom was mostly empty. • Because the alpha rays were deflected so much, the positive pieces it was striking were heavy. • Small volume and big mass = big density • This small dense positive area is the nucleus California WEB

16. The Rutherford Atom n + Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 57

17. Bohr Model of the Atom After Rutherford’s discovery, Neils Bohr proposed that electrons travel in definite orbits around the nucleus. Could not explain atomic spectra beyond hydrogen. Referred to as the planetary model (1913). Neils Bohr Planetary model

18. Quantum Mechanical Model Modern atomic theory describes the electronic structure of the atom as the probability of finding electrons within certain regions of space (orbitals). Often called the “electron cloud”

19. - e + - e + e - e + + + + e - + e e - e + e + e Models of the Atom Dalton’s model (1803) Greek model (400 B.C.) Thomson’s plum-pudding model (1897) Rutherford’s model (1909) Bohr’s model (1913) Electron-cloud model (present) 1897 J.J. Thomson, a British scientist, discovers the electron, leading to his "plum-pudding" model. He pictures electrons embedded in a sphere of positive electric charge. 1911 New Zealander Ernest Rutherford states that an atom has a dense, positively charged nucleus. Electrons move randomly in the space around the nucleus. 1926 Erwin Schrodinger develops mathematical equations to describe the motion of electrons in atoms. His work leads to the electron cloud model. 1803 John Dalton pictures atoms as tiny, indestructible particles, with no internal structure. 1913 In Niels Bohr's model, the electrons move in spherical orbits at fixed distances from the nucleus. 1800 1805 ..................... 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1932 James Chadwick, a British physicist, confirms the existence of neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons. 1924 Frenchman Louis de Broglie proposes that moving particles like electrons have some properties of waves. Within a few years evidence is collected to support his idea. 1904 Hantaro Nagaoka, a Japanese physicist, suggests that an atom has a central nucleus. Electrons move in orbits like the rings around Saturn. Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 125

20. QUARKS equal in a neutral atom Atomic Number equals the # of... Most of the atom’s mass. Subatomic Particles ATOM NUCLEUS ELECTRONS NEUTRONS PROTONS Negative Charge Positive Charge Neutral Charge Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

21. + + + + + + Mass Number • mass # = protons + neutrons • always a whole number • NOT on the Periodic Table! Neutron Electrons Nucleus Proton Nucleus Carbon-12 Neutrons 6 Protons 6 Electrons 6

22. X Mass number # protons Atomic number # protons + # neutrons mass number Nuclide Symbols Contain the symbol of the element, the mass number and the atomic number

23. + F 19 9 Nuclide Symbols • Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass number = 9 = 10 = 9 = 9 = 19

24. Br 80 35 Nuclide Symbols Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass number = 35 = 45 = 35 = 35 = 80

25. Isotopes Dalton was not exactly right. Atoms of the same element can have different numbers of neutrons Have different mass numbers Called isotopes C-12 vs. C-14 California WEB

26. Neutron Nucleus Proton Proton + Nucleus + Neutron + + + Carbon-12 + + + + + + + Carbon-14 Isotopes Electrons Nucleus Electrons Neutrons 6 Protons 6 Electrons 6 Neutrons 8 Protons 6 Electrons 6 Nucleus

27. 27 Co 58.9332 1 Nonmetals 2 3 4 M e- + M+ M 2e- + M2+ Metals 5 6 7 Metalloids N + 3e- N3- p+ = n0 = e- = 27 Co-60 Isotopes have different number of... neutrons 33 27 ISOTOPES Co-59 27 p+ = n0 = e- = 32 27 a) element symbol b) mass of isotope p+ = n0 = e- = 27 59 Ions have different number of... electrons Co2+ 32 27 25 Metals form CATIONS Nonmetals form ANIONS

28. Atomic Mass • How heavy is an atom of oxygen? • There are different kinds of oxygen atoms. • More concerned with average atomic mass. • Based on abundance of each element in nature. • Not practical to use grams because the numbers would be too small

29. + + + + + + Relative Atomic Mass • 12C atom = 1.992 × 10-23 g • atomic mass unit (amu) • 1 amu = 1/12 the mass of a 12C atom Neutron • 1 p+ = 1.007276 amu1 n0 = 1.008665 amu1 e- = 0.0005486 amu Electrons Nucleus Proton Nucleus Carbon-12 Neutrons 6 Protons 6 Electrons 6

30. Mass spectrums reflect the abundance of naturally occurring isotopes. Natural Abundance of Common Elements Hydrogen 1H = 99.985% 2H = 0.015% 12C = 98.90% 13C = 1.10% Carbon Nitrogen 14N = 99.63% 15N = 0.37% 16O = 99.762% 17O = 0.038% 18O = 0.200% Oxygen Sulfur 32S = 95.02% 33S = 0.75% 34S = 4.21% 36S = 0.02% Chlorine 35Cl = 75.77% 37Cl = 24.23% Bromine 79Br = 50.69% 81Br = 49.31%

31. Average Atomic Mass • weighted average of all isotopes • on the Periodic Table • typically rounded to 2 decimal places Avg. Atomic Mass (mass)(%) + (mass)(%) = 100 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

32. Average Atomic Mass • EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. Avg. Atomic Mass (16)(99.76) + (17)(0.04) + (18)(0.20) 16.00 amu = = 100 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

33. Average Atomic Mass Magnesium has three isotopes. 78.99% magnesium-24 with a mass of 23.9850 amu, 10.00% magnesium-25 with a mass of 24.9858 amu, and the rest magnesium-26 with a mass of 25.9826 amu. What is the atomic mass of magnesium? If not told otherwise, the mass of the isotope is the mass number in amu. 24.3023 amu California WEB

34. 29 Cu 63.548 Average Atomic Mass Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu.

35. Dmitri Mendeleev (1871) • Russian • Invented modern “Periodic Table” • Organized all known elements by properties and by atomic mass • Predicted existence of several unknown elements Dmitri Mendeleev

36. Uun 110 Uuu 111 Uub 112 Uuq 113 Uuh 116 Uuo 118 The Periodic Table Noble gases Alkaline earth metals Halogens 1 18 H 1 He 2 2 13 14 15 16 17 Li 3 Be 4 B 5 C 6 N 7 O 8 F 9 Ne 10 3 4 5 6 7 8 9 10 11 12 Na 11 Mg 12 Al 13 Si 14 P 15 S 16 Cl 17 Ar 18 Transition metals K 19 Ca 20 Sc 21 Ti 22 V 23 Cr 24 Mn 25 Fe 26 Co 27 Ni 28 Cu 29 Zn 30 Ga 31 Ge 32 As 33 Se 34 Br 35 Kr 36 Alkali metals Rb 37 Sr 38 Y 39 Zr 40 Nb 41 Mo 42 Tc 43 Ru 44 Rh 45 Pd 46 Ag 47 Cd 48 In 49 Sn 50 Sb 51 Te 52 I 53 Xe 54 Cs 55 Ba 56 * Hf 72 Ta 73 W 74 Re 75 Os 76 Ir 77 Pt 78 Au 79 Hg 80 Tl 81 Pb 82 Bi 83 Po 84 At 85 Rn 86 Fr 87 Ra 88 Y Rf 104 Db 105 Sg 106 Bh 107 Hs 108 Mt 109 * Lanthanides La 57 Ce 58 Pr 59 Nd 60 Pm 61 Sm 62 Eu 63 Gd 64 Tb 65 Dy 66 Ho 67 Er 68 Tm 69 Yb 70 Lu 71 Ac 89 Th 90 Pa 91 U 92 Np 93 Pu 94 Am 95 Cm 96 Bk 97 Cf 98 Es 99 Fm 100 Md 101 No 102 Lr 103 Y Actinides

37. The Periodic Table • Ion Formation • Atoms gain or lose electrons to become more stable. • “Isoelectronic” with the Noble Gases. 3+ 1+ NA 2+ 1- 0 3- 2- Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

38. Metals, Nonmetals, & Metalloids 1 Nonmetals 2 3 4 Metals 5 6 7 Metalloids Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 349

39. Metallic Properties metallic character increases nonmetallic character increases metallic character increases nonmetallic character increases

40. Properties of Metals, Nonmetals, and Metalloids METALS malleable, lustrous, ductile, good conductors of heat and electricity, high densities and melting points, can form alloys (2 or more metals), react with acids NONMETALS gases or brittle solids at room temperature, poor conductors of heat and electricity (insulators), low densities, low melting points METALLOIDS (Semi-metals) dull, brittle, semi-conductors (used in computer chips), mostly solids at room temperature, properties of both metals and nonmetals

41. Radioactivity • One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie(1876 - 1934). • She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

42. Radiology

43. X-rays Chest X-ray showing scoliosis corrected with steel rod

44. Radioisotopes • Radioactive isotopes • Many uses • Medical diagnostics • Optimal composition of fertilizers • Abrasion studies in engines and tires Radioisotope is injected into the bloodstream to observe circulation.

45. Characteristics of Some Ionizing Radiation Characteristics of Some Radiations Property Alpha radiation Beta radiation Gamma radiation Beta particle (electron) Alpha particle (helium nucleus) High-energy electro- magnetic radiation Composition b, e a, He-4 g Symbol -1 +2 0 Charge 1/1837 4 0 Mass (amu) Carbon-14 Radium-226 Cobalt-60 Common source 0.05 to 1 MeV 5 MeV* 1 MeV Approximate energy Moderate (4 mm body tissue) Very high (penetrates body easily) Low (0.05 mm body tissue) Penetrating power Metal foil Paper, clothing Lead, concrete (incomplete shields) Shielding *(1 MeV = 1.60 x 10-13 J)

46. Absorption of Radiation Timberlake, Chemistry 7th Edition, page 84

47. 10 5 13 7 1 0 4 2 n N B He = neutrons = protons Alpha Radiation + stable isotope bombarding particle new radioactive isotope neutron Timberlake, Chemistry 7th Edition, page 92

48. Alpha Decay (Emission)(unstable isotope decays) alpha particle radioactive isotope neutron proton Timberlake, Chemistry 7th Edition, page 87

49. Beta Decay (Emission)(neutron in unstable nucleus emits electron and changes to proton) Timberlake, Chemistry 7th Edition, page 90

50. Alpha Decay Beta Decay Alpha and Beta Decay (Emission)