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AN INTRODUCTION TO CHEMISTRY

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  1. AN INTRODUCTION TO CHEMISTRY Science 2009 – 2010 Academic Decathlon

  2. A Brief History of Chemistry In this section, we will cover: Chemistry prior to the Scientific Revolution Antoine Lavoisier and the Birth of Modern Chemistry Chemistry After Lavoisier Ten Independent Research Topics, including Mixing Metals and Radioactivity

  3. Chemistry Prior to the Scientific Revolution • Gold → copper → tin and bronze • Iron: • Meteorites? • Mixed with carbon to form steel • Glass and pottery: decoration, utility

  4. IRT: Mixing Metals to Make Bronze • Bronze: 90% copper, also arsenic, tin, antimony, lead • First used by Sumerians (3600 BCE) • Used for weapons, decoration • Methods: open casting, “lost-wax” • Superior Chinese alloys → effective defense

  5. IRT: The Use of Dyes and Preservatives • Cave paintings and Egyptian tombs → Roman Empire, Phoenicians, Minoan Crete • Woad, indigo, oxides of mercury, Tyrian purple • Mummy wrappings, stained glass, linen and hemp

  6. IRT: Alchemy and the “Philosopher’s Stone” • Transmutations: base metals into gold • Practiced as a science from 331 BCE to roughly 300 CE • Philosopher’s Stone: • Transmutations • Elixir of Life

  7. IRT: Gunpowder and Fireworks • Saltpeter, charcoal, sulfur • Invented by Chinese before 1100 CE • Roger Bacon recipe: Opus Tertium • Sent to Pope • Rockets, projectiles → cannons • Battle of Crecy: 1346 CE

  8. IRT: Early Thinkers on the Nature of Matter • Aristotle: • Ideas from Plato (used term “element”) et al • Four properties: hot, cold, wet, dry • Four elements: fire, air, water, earth • Fifth element: ether • Democritus: • Small discrete particles • Properties of these “atoms”?

  9. Antoine Lavoisier and the Birth of Modern Chemistry • Notable chemists 16th-early 19th century: • Johann Baptista van Helmont, Robert Boyle, Joseph Black, Henry Cavendish, Joseph Priestly • Antoine Lavoisier: coherent gathering of current theories (nature of air, oxidation, water, matter) • Involved in French Revolution, targeted by Jacobins

  10. IRT: The “Living Tree” Experiment • Johann Baptista van Helmont • Living systems • Tree growing out of “water onely” [sic] • Tree weight vs. soil weight

  11. IRT: Antoine Lavoisier and His Role and Fate in the French Revolution • Born to a wealthy lawyer, studied accounting and law • President of a bank, member of the Ferme Generale (private tax collection agency) • Supported the new regime during/after revolution • Targeted and executed → links to chemistry and old regime

  12. IRT: Madame Lavoisier • Marie Anne Pierrette Paulz married Antoine Lavoisier in 1771 • Father was in the Ferme Generale • Learned chemistry and English to assist in lab • Arrested and held for 65 days by Jacobins in power • Remarried in 1805, then divorced, died alone

  13. Chemistry After Lavoisier • Henri Becquerel: radioactivity • Pierre and Marie Curie: radioactive decay • J.J. Thompson: electron • Ernest Rutherford: atomic nucleus • James Chadwick: neutron • Niels Bohr: electron orbitals • Frederick Soddy: isotopes

  14. IRT: Radioactivity and Nuclear Structure • Henri Becquerel: radioactive decay with photographic plates, 1896 • Pierre and Marie Curie: radioactivity and two new elements (polonium, radium), 1898 • Ernest Rutherford: alpha particles and atomic structure, 1920 • James Chadwick: neutron, 1932

  15. Chemistry After Lavoisier • Albert Einstein: photoelectric effect • Louis de Broglie and Erwin Shroedinger: quantum energy relationships • Periodic Table • Inter-/Intramolecular Forces • Dipoles • Heat, Work, Temperature • Reactants, Products, Chemical Kinetics

  16. IRT: The Periodic Table and Associated Periodicity • Dmitri Mendeleev • Repeating properties among elements • Issues with ordering by weight • Re-measuring and skipping positions helped • Henry Moseley: ordering by atomic numbers

  17. Wrap-Up • Both times of peace and war brought about advancements in chemistry • Antoine Lavoisier and those like him were vital to the development of modern chemistry • Chemistry since Lavoisier has developed rapidly across many fields

  18. The Structure of Matter In this section, we will cover: Atomic Theory and Structure Chemical Bonding and Intermolecular Forces Molecular Models Nuclear Chemistry Ten Independent Research Topics, including Electronegativity and Fission and Fusion Reactions

  19. Atomic Theory and Atomic Structure • Atomic structure dictates element chemical behavior • Positive, negative, neutral particles • Weight of one atom determined by weighing many atoms • Mass spectrometers: accuracy

  20. IRT: Mass Spectrometry • Separates and measures compounds • Main components: • Ion source • Mass analyzer • Detector • Curved magnet or cycling magnetic field

  21. Atomic Theory and Atomic Structure: Mass and Isotopes • Atomic number: protons • Atomic mass: protons + neutrons • Same element with different numbers of neutrons: isotopes • Carbon: atomic standard (12 amu) • Weighted averages: • (isotope A abundance x isotope A weight) + (isotope B abundance x isotope B weight)

  22. IRT: Properties and Importance of Commonly Recognized Isotopes • 21H (Deuterium): • Tracer isotope • Fusion reaction with tritium • 146C: • Radiocarbon dating • Climate change studies • 6027Co: • Highly radioactive: kills cancer cells and bacteria • Examines steel components

  23. Atomic Theory and Atomic Structure: Electrons • Absorption or emission spectrum: determining structure of an atom • Bohr Model of the atom: fixed orbits • Quantum Mechanical Model: non-fixed orbits • Electron clouds: orbits (s and p) • Orbital shapes determine bonding behaviors

  24. IRT: Wave and Particle Nature of the Electron and Photon • All matter exhibits both wave and particle properties • Light as a particle: photoelectric effect • Electrons as energy: Davisson-Germer experiment

  25. Atomic Theory and Atomic Structure:The Periodic Table • Number of orbits determine period • Across a row (period): • Atomic radius decreases • Ionization energy increases • Electron affinity increases

  26. Atomic Theory and Atomic Structure: The Periodic Table • Down a column (group or family): • Atomic radius increases • Ionization energy decreases • Electron affinity decreases

  27. IRT: Electronegativity • One atom’s net attraction of electrons from the adjacent atom to which it is chemically bonded • Higher value = greater attraction • Increases up a group and across a period • Fluorine → most strongly electronegative • Values predict “winners”

  28. Chemical Bonding and Intermolecular Forces: Intramolecular Forces • Ionic: • Electron transfer • NaCl • Covalent: • Sharing electrons • CH4 • Metallic: • Electron sea • Brass

  29. Chemical Bonding and Intermolecular Forces: Intermolecular Forces • Van der Waals force: uneven distribution of positive and negative charges (temporary or permanent) • Hydrogen bonds: strongly electronegative atom bonded to hydrogen on another molecule

  30. IRT: The Importance of Hydrogen Bonding in Living Systems • DNA contains hydrogen, oxygen and nitrogen • Hydrogen bonds in DNA create its double helix structure

  31. Chemical Bonding and Intermolecular Forces: Effects and Properties of Bonds • Solid structures: • Ionic lattice • Covalent network or molecular solid • Translational motion • Strength of force determines state at room temperature • Uneven bonds are polar

  32. Molecular Models: Lewis Structures • G.N Lewis (1875-1946) • Lewis Structures • Dots represent electrons • Valence electrons (bonding) • Bonding pairs and non-bonding (“lone”) pairs

  33. Valence Bonds and Hybridization • Single bond • One overlap between orbitals • Double-bond or triple-bond • Multiple overlaps • Hybridization • Different orbital shapes combine to form a new shape

  34. IRT: The Formation of Molecular Orbitals • Orbitals are electron waves in particular positions and shapes • Sigma (s) orbitals • Overlap concentrated along an imaginary connecting line between nuclei • Pi (p) orbitals • Overlap concentrated away from connecting line between nuclei

  35. IRT: The Formation of Molecular Orbitals • N2: one sigma and two pi bonds • O2: one sigma and one pi bond • F2: one sigma bond • CO2: one sigma and one pi bond for each oxygen atom

  36. Molecular Models: VSEPR Models • Valence Shell Electron Pair Repulsion model • Three dimensions • Molecular geometry (tetrahedron, linear, et al)

  37. IRT: The Resonance Concept Model • Explains bond properties in mathematically uneven bonds • Sharing, delocalizing and distributing electrons to satisfy the octet • O3 and SO3

  38. Molecular Models: Oxidation States • Assigned based on electron loss/gain • H2O: H = +1 O = -2 • Sum of oxidation numbers in neutral molecule equals zero • Sum of oxidation numbers in charged molecule equals total charge

  39. Molecular Models: Dipole Moments and Polarity • Dipole moment • Lack of symmetry • Bond dipoles do not cancel each other out • Polar molecules • High polarity → strong van der Waals forces • Stronger bonds • Higher boiling and melting points

  40. Nuclear Chemistry • Radioactive atoms • Unstable nuclei (varying ratios of neutrons to protons) • Regain stability through various pathways • Alpha decay: loss of helium nucleus • Beta decay: neutron → proton • Positron decay: proton → neutron

  41. IRT: Decay Equations and Predicting Products of Decay – Alpha • Alpha decay • Very large nuclei • Atoms of bismuth and those larger • Sample: • 23892U  →  23490Th  +  42He2+

  42. IRT: Decay Equations and Predicting Products of Decay – Beta and Positron • Beta (beta-minus) decay: • Too many neutrons • Sample: • 32H → 31He+ electron + antineutrino • Positron (beta-plus) decay: • Too many protons • Sample: • 104C → 105B + positron + neutrino

  43. IRT: Alpha Bombardment Reactions • Ernest Rutherford: 1919 • Nuclear transformations can be caused by bombardment (including alpha bombardment) • Example: • 42He + 147N → 178O + 11H

  44. IRT: Fission and Fusion Reactions • Example fission of uranium-235: • 23592U143 + neutron → 13454Xe80 + 10038Sr62 + neutron + neutron • Products vary (typically amu of 130 and 100 plus 2-3 neutrons) • Hydrogen-2 and Hydrogen-3 fusion: • 21H1 + 31H1 → 42He2 + neutron • Not yet feasible for large-scale power

  45. Wrap-Up • Various notations and models are used to express and explain atomic structure and bonds • Bonds vary in composition, type, structure and polarity • Lewis and VSEPR models help visually express molecular orientation and geometry • Nuclear chemistry involves radioactivity and decay reactions of various types

  46. States of Matter In this section, we will cover: Gases, Liquids and Solids Phase Diagrams Solutions Four Independent Research Topics, including Carbon Dioxide and Raoult’s Law

  47. Gases: Laws of Ideal Gases • Boyle’s Law: P x V = a constant (C) • Charles’ Law: V/T = a constant (D) • Combination: PV/T = CD • Tracking changes: • (P1V1)/T1 = (P2V2)/T2

  48. IRT: Partial Pressures and Correction of Gas Volumes Collected Over Water • Gas proportions in mixtures → expressed in mole fractions • Dalton’s Law: • Mole fraction A = Pressure of A / Total Pressure • Gas container over water • Water vapor pressure relies only on temperature • Total pressure – water vapor pressure = gas pressure

  49. Gases: Kinetic Molecular Theory • Four major assumptions about ideal gases: 1. A pure gas consists of tiny, identical molecules 2. The molecules move very rapidly in all directions but at different speeds 3. No forces of repulsion or attraction exist between the molecules 4. Gas pressure is a result of collisions of the molecules with the walls of the container (no loss of energy)

  50. Gases: Particle Speed • Average molecule speed (u) determines frequency of collisions with given side length (l) • Momentum change from collisions determines force • Molecule mass = m • Force = (mu2)/l • Number of molecules = N • Pressure = (1/3)((Nmu2)/V) or PV = (1/3)Nmu2