2. The evolution of Atomic Theory The evolution of Atomic Theory Dalton’s Atomic Theory Development of structure of the atom Nucleus Dimitri Mendeleev(Periodicity) Modern periodic tableperiodic table New model of the atom

3. Chemistry Timeline #1 B.C. 400 B.C. Demokritos and Leucippos use the term "atomos” 1500's  Georg Bauer: systematic metallurgy  Paracelsus: medicinal application of minerals 1600's Robert Boyle:The Skeptical Chemist. Quantitative experimentation, identification of elements 1700s'  Georg Stahl: Phlogiston Theory  Joseph Priestly: Discovery of oxygen  Antoine Lavoisier: The role of oxygen in combustion, law of conservation of mass, first modern chemistry textbook  2000 years of Alchemy

4. Chemistry Timeline #2 1800's  Joseph Proust: The law of definite proportion (composition)  John Dalton: The Atomic Theory, The law of multiple proportions  Joseph Gay-Lussac: Combining volumes of gases, existence of diatomic molecules  Amadeo Avogadro: Molar volumes of gases  Jons Jakob Berzelius: Relative atomic masses, modern symbols for the elements  Dmitri Mendeleyev: The periodic table  J.J. Thomson: discovery of the electron  Henri Becquerel: Discovery of radioactivity 1900's  Robert Millikan: Charge and mass of the electron  Ernest Rutherford: Existence of the nucleus, and its relative size  Meitner & Fermi: Sustained nuclear fission  Ernest Lawrence: The cyclotron and trans-uranium elements

5. Dalton’s Atomic Theory (1808)  Atoms cannot be subdivided, created, or destroyed  Atoms of different elements combine in simple whole-number ratios to form chemical compounds  In chemical reactions, atoms are combined, separated, or rearranged  All matter is composed of extremely small particles called atoms  Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties John Dalton

6. Modern Atomic Theory Several changes have been made to Dalton’s theory. Dalton said: Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties Modern theory states: Atoms of an element have a characteristic average mass which is unique to that element.

7. Modern Atomic Theory #2 Dalton said: Modern theory states: Atoms cannot be subdivided, created, or destroyed Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions!

8. Law of conservation of matter Law of conservation of matter When a chemical change(reaction) takes place, matter is neither created nor destroyed. Antoine Lavoisier (1775)

9. Law of definite Proportions When two elements react to form a compound, the total amount(mass) of the compound formed is determined by the composition of the compound and not by the masses of the elements used.

10. Example If 50.0 g of water is decomposed into 5.6 g of hydrogen gas and 44. 4g of oxygen gas. What is the percent by mass of these elements?

11. Law of multiple proportions When two elements (a and b) can combine to form more than one compound, then for a fixed weight of a, the weights of b in two different compounds always form a ratio that is expressible in small whole numbers.

12. Development of the structure of the atom Electron (e-) Thomson,1897 present in all atoms, negative charge(-1), 1/1836 mass of H atom Proton (p+) Thomson and Goldstein,1907 Present in all atoms, about the same mass of H, charge (+1) Neutron (n o ) Chadwick, 1932 Same mass as proton, 0 charge

13. Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

14. Thomson’s Experiment A stream of charged particles flows from cathode to the anode Voltage source - + Vacuum tube Metal Disks

15. Thomson Experiment Voltage source n Passing an electric current makes a beam appear to move from the negative to the positive end - +

16. Thomson’s Experiment Voltage source + - n By adding an electric field

17. Thomson’s Experiment Voltage source + - n By adding an electric field he found that the moving pieces were negative

18. Thomson’s Atomic Model Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

19. What did Thomson conclude from his experiment? He concluded that a cathode ray is composed of particles with a negative charge. These particles are electrons.

20. Mass of the Electron 1909 – Robert Millikan determines the mass of the electron. The oil drop apparatus Mass of the electron is 9.109 x 10 -31 kg

21. Chapter 2 The Discovery of Atomic Structure Cathode Rays and Electrons Consider the following experiment: Oil drops are sprayed above a positively charged plate containing a small hole. As the oil drops fall through the hole, they are given a negative charge. Gravity forces the drops downward. The applied electric field forces the drops upward. When a drop is perfectly balanced, the weight of the drop is equal to the electrostatic force of attraction between the drop and the positive plate.

22. The Discovery of Atomic Structure Cathode Rays and Electrons

23. Conclusions from the Study of the Electron  Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.  Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons  Electrons have so little mass that atoms must contain other particles that account for most of the mass

24. Atomic Particles ParticleChargeMass (kg)Location Electron9.109 x 10 -31 Electron cloud Proton+11.673 x 10 -27 Nucleus Neutron01.675 x 10 -27 Nucleus

25. Rutherford’s Gold Foil Experiment  Alpha particles are helium nuclei  Particles were fired at a thin sheet of gold foil  Particle hits on the detecting screen (film) are recorded

26. Nucleus: holds protons and neutrons. Rutherford’s gold foil experiment “It was… as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you”

27. Try it Yourself! In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

28. The Answers Target #1Target #2

29. The Atomic Scale  Most of the mass of the atom is in the nucleus (protons and neutrons)  Electrons are found outside of the nucleus (the electron cloud)  Most of the volume of the atom is empty space “q” is a particle called a “quark”

30. About Quarks… Protons and neutrons are NOT fundamental particles. Protons are made of two “up” quarks and one “down” quark. Neutrons are made of one “up” quark and two “down” quarks. Quarks are held together by “gluons”

31. Rutherford’s Findings  The nucleus is small  The nucleus is dense  The nucleus is positively charged  Most of the particles passed right through  A few particles were deflected  VERY FEW were greatly deflected Conclusions:

32. The structure of the atom Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei X A Z H 1 1 H (D) 2 1 H (T) 3 1 U 235 92 U 238 92 Mass Number Atomic Number Element Symbol

33. Atomic Masses IsotopeSymbolComposition of the nucleus % in nature Carbon-12 12 C6 protons 6 neutrons 98.89% Carbon-13 13 C6 protons 7 neutrons 1.11% Carbon-14 14 C6 protons 8 neutrons <0.01% Atomic mass is the average of all the naturally isotopes of that element. Carbon = 12.011

34. Law of Mendeleev Properties of the elements recur in regular cycles(periodically) when the elements are arranged in order of increasing atomic weight

35. Mendeleev’s Periodic Table Dmitri Mendeleev

36. Modern Periodic Table Vertical columns (groups) Horizontal rows (periods) Group IA-VIIIA representative or main group of elements Group IB-VIIIB are transition metals Green rows at the bottom: (rare earth metals) Lanthanides and Actinides

38. The Periodic Table Period Group or family Period Group or Family

39. Easily lose valence electron (Reducing agents) React violently with water Large hydration energy React with halogens (group viiA) to form salts The Properties of a Group: the Alkali Metals

40. Properties of Metals  Metals are good conductors of heat and electricity  Metals are malleable  Metals are ductile  Metals have luster

41. Properties of Nonmetals Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element. Nonmetals are poor conductors of heat and electricity Nonmetals tend to be brittle Many nonmetals are gases at room temperature

42. Properties of Metalloids Metalloids straddle the border between metals and nonmetals on the periodic table.  They have properties of both metals and nonmetals.  Metalloids are more brittle than metals, less brittle than most nonmetallic solids  Metalloids are semiconductors of electricity  Some metalloids possess metallic luster

43. Silicon, Si – A Metalloid  Silicon has metallic luster  Silicon is brittle like a nonmetal  Silicon is a semiconductor of electricity Other metalloids include:  Boron, B  Germanium, Ge  Arsenic, As  Antimony, Sb  Tellurium, Te

44. Atomic size Atomic radius(measured by experimental techniques) measured in angstroms(10 -10 meter), nanometers(nm, 10 -9 ) or picometers(pm, 10 -12 ) In a group, as you move down the atoms get larger(there are exceptions) Across a period from left to right the atoms get smaller

45. Half of the distance between nuclei in covalently bonded diatomic molecule "covalent atomic radii" Periodic Trends in Atomic Radius Radius decreases across a period Radius increases down a group Determination of Atomic Radius:

46. Ionic Radii Cations (+) Positively charged ions formed when an atom of a metal loses one or more electrons Smaller than the corresponding atom Anions (-)  Negatively charged ions formed when nonmetallic atoms gain one or more electrons  Larger than the corresponding atom ( the extra repulsion produced by the incoming electron causes the atom to expand)

48. Predicting Ionic Charges Group 1: Lose 1 electron to form 1+ ions H+H+H+H+ Li + Na + K+K+K+K+

49. Predicting Ionic Charges Group 2: Loses 2 electrons to form 2+ ions Be 2+ Mg 2+ Ca 2+ Sr 2+ Ba 2+

50. Predicting Ionic Charges Group 13: Loses 3 Loses 3 electrons to form 3+ ions B 3+ Al 3+ Ga 3+

51. Predicting Ionic Charges Group 14: Loses 4 Loses 4 electrons or gains 4 electrons Caution! C 2 2- and C 4- are both called carbide

52. Predicting Ionic Charges Group 15: Gains 3 Gains 3 electrons to form 3- ions N 3- P 3- As 3- Nitride Phosphide Arsenide

53. Predicting Ionic Charges Group 16: Gains 2 Gains 2 electrons to form 2- ions O 2- S 2- Se 2- Oxide Sulfide Selenide

54. Predicting Ionic Charges Group 17: Gains 1 Gains 1 electron to form 1- ions F 1- Cl 1- Br 1- Fluoride Chloride Bromide I 1- Iodide

55. Predicting Ionic Charges Group 18: Stable Noble gases do not form ions! Stable Noble gases do not form ions!

56. Ionization Energy Minimum amount of energy required to remove the outermost electron from an atom (IE) IE decreases as you go down a group IE increases as you go from left to right in a period

58. Electronegativity A measure of the ability of an atom in a chemical compound to attract electrons Electronegativities tend to increase across a period Electronegativities tend to decrease down a group or remain the same

59. Summation of Periodic Trends

60. New model of the atom New model came from closer examinations of properties of light given off by gaseous atoms Light could be defined as particles or pockets of energy called photons or as waves of energy. As a wave it is characterized by lambda(λ) Lambda= distance between identical adjacent points on the wave(distance between one crest or trough)

61. Visible light ranges from 380-750nm The visible and invisible wavelengths are called electromagnetic radiation The entire spectrum=electromagnetic spectrum The white light dispersed by a prism into different wavelengths gives the continuous spectrum.