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  • 1. Chemical Building Blocks: Atomic Theories, Models, and Electronic Structure
  • 2. Outline 1. A Brief History  Pre-atomic view of matter  The Greek Idea  Lavoisier: Conservation of Mass  Proust: Definite Proportions  Dalton: Atomic Theory 2. Electricity and the Atom 3. X-rays and Radioactivity 4. Atomic Models  Rutherford’s nuclear model  Structure of the nucleus  The Bohr model and electronic arrangement 5. The Quantum Model  Electronic configuration  Quantum numbers
  • 3. Pre-Atomic View of Matter Matter was seen as continuous, as the four Greek elements were. No distinct divisions between fire, water, earth, air Mixtures of the four gave the properties of being hot or cold, moist, or dry
  • 4. EARLY THOUGHTS ON MATTER  LEUCIPPUS: “There must  DEMOCRITUS: Referred to be tiny particles of water these particles as atomos; that could not be Each atom was distinct in subdivided.” Observe the size and shape (eg. Water SAND. as round balls, Fire as sharp)
  • 5. EARLY THOUGHTS ON MATTER  ARISTOTLE: Matter was continuous, not atomistic  Five centuries after, the Roman LUCRETIUS wrote a poem, “On the Nature of Things,” where strong arguments for the atomic nature were presented  Late 1600’s, ROBERT BOYLE publishes The Sceptical Chymist. Proper experimentation can show if theory is valid. Introduction of ELEMENT and COMPOUND
  • 6. LAVOISIER: Conservation of Mass  Antoine Laurent Lavoisier  “When a chemical reaction is carried out in a closed system, the total mass of the system is not changed.”  Red mercuric oxide  Mercury + OXYGEN  1st to use systematic names; 1st chem bk. ; “father”  Experiments with burning coal (combustion), and breathing guinea pigs (respiration). We cannot create  LAW: Matter is neither created nor from nothing. destroyed in a chemical change. The total mass of the reaction Chemistry is products is always equal to the total about mass of the reactants transformation.
  • 7. Proust: Definite Proportions  Joseph Louis Proust: Copper carbonate always had the same composition  LAW OF DEFINITE PROPORTIONS or CONSTANT COMPOSITION: A compound always contains the same elements in certain definite proportions and in no other combinations.  J.J.Berzelius: Prepared an extensive list of atomic weights; Lead sulfide experiments  Henry Cavendish: 1783;  Hydrogen gas + Oxygen gas  Water  1800: Volta designed a powerful battery W.Nicholson and A.Carlisle would use to separate water into its elements.
  • 8. Dalton: Law of Multiple Proportions  Elements could combine in in more than one set of proportions.  If elements A and B react to form two different compounds, the masses of B combined with a fixed mass of A, can be expressed as a ratio of small whole numbers
  • 9. Dalton’s Atomic Theory  Matter is composed of extremely small particles called atoms. p All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements.  Compounds are composed of atoms of different elements combined in fixed proportions. p Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.
  • 10. 2
  • 11. 16 X + 8Y 8 X2Y
  • 12. ELECTRICITY and the ATOM  ELECTROLYSIS  CATHODE RAY TUBES  William Crookes passed an electric current through a tube with air at low pressure. The tube has metal electrodes and the beam of current is seen as green fluorescence when it strikes the Zinc fluoride coated screen
  • 13. J.J. Thomson, measured mass/charge of e- (1906 Nobel Prize in Physics) 2.2
  • 14. Thomson’s Experiment: M/C  Were the rays beams of particles or did it consist of energy, much like light?  1897: Joseph John Thomson  Cathode rays are deflected in an electric field. Attracted by POSITIVE, deflected by NEGATIVE.  Particles were the same regardless of the electrodes or gas.  What would he conclude, then?
  • 15. Foundations of Atomic Theory Law of Conservation of Mass Mass is neither destroyed nor created during ordinary chemical reactions. 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. 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.
  • 16. Law of Definite Proportions Whether synthesized in the laboratory or obtained from various natural sources, copper carbonate always has the same composition. Analysis of this compound led Proust to formulate the law of definite proportions. + + 103 g of 53 g of 40 g of oxygen 10 g of carbon copper carbonate copper
  • 17. Law of Multiple Proportions John Dalton (1766 – 1844) If two elements form more than one compound, the ratio of the second element that combines with 1 gram of the first element in each is a simple whole number. e.g. H2O & H2O2 water hydrogen peroxide Ratio of oxygen is 1:2 (an exact ratio)
  • 18. Cathode Ray Tube 2.2
  • 19. Plum-Pudding Model Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56
  • 20. Thomson’s Calculations Thomson PAPER Cathode Ray Experiment  Thomson used magnetic and electric fields to measure and calculate the ratio of the cathode ray’s mass to its charge. charge of electric length of length of Electric ray particle x field x deflection region x drift region = deflection mass of ray velocity of 2 x particle ray particle charge of magnetic length of length of Magnetic ray particle x field x deflection region x drift region = deflection mass of ray velocity of x particle ray particle magnetic deflection magnetic field = x velocity electric deflection electric field
  • 21. Measured mass of e- (1923 Nobel Prize in Physics) e- charge = -1.60 x 10-19 C Thomson’s charge/mass of e- = -1.76 x 108 C/g e- mass = 9.10 x 10-28 g
  • 22. ROENTGEN RAYS  WILHELM CONRAD ROENTGEN  1895  Working in a darkroom on the glow produced in certain substances by cathode rays  He noticed the glow also occurring on a chemically-treated piece of paper (even in next room). The “ray” could travel through walls!  When he waved his hand between the radiation source and the glowing paper, he could see the bones of his own hand on the paper. X-RAYS
  • 23. Discovery of Radioactivity  ANTOINE HENRI BECQUEREL  1895  Studied fluorescence by 1. Wrap photographic film in black paper 2. Place fluorescing crystals on top 3. Place paper in strong sunlight i. Like ordinary light: would not pass through paper ii. Like X-rays: would pass and fog the film 4. Work with URANIUM: always fogging the film! 5. Perhaps, radiation coming from uranium was unrelated to fluorescence but a characteristic of uranium.  MARIE SKLODOWSKA: coined the term “Radioactivity”: the spontaneous emission of radiation from certain unstable elements
  • 24. The CURIES  MARIE SKLODOWSKA married PIERRE CURIE, a French Physicist and discover radioactive polonium and radium  1903 Nobel in Physics (Becquerel, Curie, Curie)  Marie Curie: 2nd Nobel prize in 1911
  • 25. TYPES OF RADIOACTIVITY  Three types of radiation emanated from these radioactive elements,  ERNEST RUTHERFORD, a New Zealander, chose the names alpha, beta, and gamma for these.  ALPHA: beams of positive particles (identical to He2+ ions  BETA: negatively-charged; identical to cathode rays; therefore, an electron  GAMMA: not deflected; penetrating; a form of energy
  • 26. (Uranium compound)
  • 27. Health Effects of Ionizing Radiation
  • 28. REM – roentgen equivalent man Degree of exposure How much time? 5-25:genetic damage. genetic damage in 18-90s 50:alter white blood cells. 75-125: radiation alteration of white blood sickness. cells in 3 minutes 400: kill 50% of exposed people radiation sickness in 5-8 500-600 :will kill almost minutes all exposed people. death in 35-60 minutes.