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Atoms, E lements and Quantum Mechanics 01 and 06 October 2015

Atoms, E lements and Quantum Mechanics 01 and 06 October 2015. Physics Chemistry Astronomy Geology/Ecology Biology. Topics. Discovery of atomic structure and function Models of atoms Thompson and Rutherford atom (~1900) Bohr atom (1913)

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Atoms, E lements and Quantum Mechanics 01 and 06 October 2015

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  1. Atoms, Elements and Quantum Mechanics01 and 06 October 2015 Physics Chemistry Astronomy Geology/Ecology Biology

  2. Topics • Discovery of atomic structure and function • Models of atoms • Thompson and Rutherford atom (~1900) • Bohr atom (1913) • Quantum mechanics (1930’s) • Elements, atoms and the Periodic Table • Electrons in orbits nested within shells • Valence electrons

  3. Some Notations on the Syllabus • Delete: Chemical reactions (pp. 223-227) Chapter 11: Materials and Properties (pp. 237-259)

  4. Crystal Morphology and Color: Structure of the Atom

  5. Leaf Color:Structure of the Atom

  6. Eye Color:Structure of the Atom

  7. Compounds to Quarks: A Hierarchy Compound Element Atom Subatomic Particle Quarks (Higgs) Hierarchy theory and emergent properties

  8. Thompson’s Investigation of the Electron (1870’s) • Idea: smaller components comprise atoms • Hypothesis: Atoms consist of components, one of which is negatively charged with a very small mass • Testing the hypothesis

  9. Thompson’s Experiment Hypothesis:Atoms consist of components, one of which is negatively charged with a very small mass Methodology Observations: 1. Deflection of negatively- charged beam 2. Very small mass 3. Mass same for all elements Hypothesis:Accept Particle name:Electron

  10. Rutherford’s Investigation of the Nucleus (1910) • Idea: other smaller components are part of atoms too, including ones that are positively charged • Hypothesis: Atoms consist of multiple subcomponents, one of which is positive in charge • Testing the hypothesis • Alpha particles (+), gold foil, “bullets”, and “tracks” http://www.youtube.com/watch?v=5pZj0u_XMbc

  11. Observations, Hypothesis, Conclusion and a Revised Model • Observations • Almost all alpha’s (+) passed through foil unaffected • Very small number of alpha’s (+) deflected at a small angle • 1/1,000 bounced back • Hypothesis: Atom consists of a (i) positive component that is (ii) small in volume in comparison to atom itself • Accept/reject? • Conclusions • Name of particle is the proton • Electrons circling the nucleus • Shortcomings of the new model?

  12. Resolving Shortcoming of the Model: Atomic Structure and the Bohr Atom • Observations (1913) • Heat hydrogen gas and light emitted as a discrete wavelengths (not continuous spectrum) • Other gases behave the same in producing discrete wavelength • But, each gas is unique in emitted (e.g., violet versus yellow versus red versus green)

  13. Bohr’s Hypothesis and Model Quantum Concepts 1. Only discrete orbits for electrons 2. Discrete frequency of photon (emitted light) 3. Explains spectroscopic properties of elements

  14. Quantum Behavior and Spectroscopy

  15. Application of Spectroscopy: Elemental Analysis

  16. Bohr’s Model of the Atom • Building on predecessor models: • Thompson’s electron • Rutherford’s nucleus and protons • Electrons in orbits • Orbits exhibit discrete quantum structure/layers • When excited, electrons release energy in discrete packets of energy (photons of light) • Sequel to Bohr’s atom (2-3 decades): quantum mechanics

  17. Bohr’s Atom and Spectroscopy

  18. Electrons as Particles and Waves: Wave-Particle Duality http://www.youtube.com/watch?v=DfPeprQ7oGc

  19. Theory of Quantum Mechanics • Observations • Quantum behavior of electrons in Bohr model (orbits, etc.) • Wave-particle duality of electrons • Key: integrated mechanisms of waves and particles, focusing on “fuzzy electron clouds” • Hypothesis: new evolving model of atomic structure: quantum mechanics theory of the atom • Incorporation of parts of predecessor • Plus: wave properties of electrons in orbits

  20. Topics • Discovery of atomic structure and function • Models of atoms • Thompson and Rutherford atoms • Bohr atom (1913) • Quantum mechanics (1930’s) • Elements, atoms and the Periodic Table • Electrons in orbits nested within shells • Valence electrons

  21. Elements • Patterns • 92 naturally occurring elements (e.g., hydrogen, gold, helium) • Total of 113+ • 25 of 92 are essential to life (e.g., what are they?) • Key points • any element is the same in its chemical structure and physical properties (stable over time, with one exception - radioactive elements) • All elements have origin in either the big bang (hydrogen and helium) or the subsequent evolution of the universe (Dr. Geller will speak to this a bit later)

  22. Atomic NoSymbolName 1 H Hydrogen 2 He Helium 6 C Carbon 7 N Nitrogen 8 O Oxygen 17 Cl Chlorine 18 Ar Argon 26 Fe Iron 53 I Iodine 79 Au Gold 80 Hg Mercury 94 Pu Plutonium 104 Rf Rutherfordium

  23. Topics • Discovery of atomic structure and function • Models of atoms • Thompson and Rutherford atoms • Bohr atom (1913) • Quantum mechanics (1930’s) • Elements, atoms and the Periodic Table • Electrons in orbits nested within shells • Valence electrons

  24. Elements and Compounds • Compound • Elements combine in recurrent, precise and predictable ways • Sodium + Chlorine = Sodium Chloride Na + Cl = NaCl metal + gas = solid • Key points • Atoms of sodium (Na) and chlorine (Cl) remain atoms of each respective element • Product (NaCl) is recurrent and predictable • Emergentproperty: “emergence” of new properties in a compound not predicted by the summation of the two elements (hierarchy theory) • Other example: Hydrogen + oxygen = __________

  25. Subatomic Particles • Atoms composed of subatomic particles • Most stable particles • Neutrons • Protons • Electrons • Other less stable and understood particles (quarks, etc. … Dr. Geller will speak to this later) • Relationship among the more stable particles NeutronProton Electron Charge neutral positive negative Mass 2 x 10-24 g 2 x 10-24 g 5 x 10-28 g

  26. What is Right About this Model?What is Not Right About this Model?

  27. Electrons in Orbits

  28. Electrons • Energy “barons” of the atom (motion and in orbits) • Energy = ability to do work • Potential energy = energy stored due to position or location (i.e., orbits) • Charge is negative (-) and particle is “in motion” in a quantum sense

  29. Key to Electron Structure • Count the number of protons: number of electrons = number of protons (why?) • Electrons are negative in charge and act as particles and waves in a quantum sense • Electrons are in motion around the nucleus in “orbits” that are discrete • Only two electrons exist in a given orbit (Pauli’s Exclusion Principle)

  30. Electrons • Example of Sulfur (1632S) (16 electrons in 3 shells) What are shells, what are orbits and who is Pauli?

  31. Orbits, Shells and Electrons http://www.colorado.edu/physics/2000/applets/a2.html

  32. Example of Electrons in Shells As electrons move among shells, they change potential energy • Hot summer day, bright sun and car top • Light absorption by pigments and electrons “jump” to higher shell (potential energy); give off energy when they drop back (kinetic/heat energy) • Banana, orange juice or bagel this AM (how about a granola bar)? • Excited electron “captured” by chlorophyll in leaf and shuttled to a sugar molecule in its excited state (potential energy) until you release the energy via digestion, allowing the electron to “drop back” to a lower orbit (kinetic/chemical/heat energy)

  33. Some Keys to Electron Structure • Electrons reside in shells as a function of quantum mechanics (1-4 orbits per shell) • Never more than two electrons per orbit (Pauli’s Exclusion Principle) • Distribution of electrons is key to understanding why elements and atoms behave the way they do • Outermost electrons are called valence electrons; special significance in chemistry

  34. Periodic Table of Elements • Concept: most stable state for an atom = outermost shell filled with maximum number of electrons • 1st Shell (1 orbit; 2 electrons) • Hydrogen (11H; 1 electron; stable ?) • Helium (24He; 2 electrons; stable ?) • Periodic Table’s 1st Row • Hydrogen and Helium

  35. Orbits, Shells and Electrons http://www.colorado.edu/physics/2000/applets/a2.html

  36. Atomic Structure: Periodic Table Stable Unstable

  37. Periodic Table

  38. Periodic Table of Elements • 2nd shell has 4 orbits with 2 electrons (maximum) per orbit (total of 8 electrons/shell) • Most stable configuration is: • 1st shell filled with 2 electrons • 2nd shell filled with 8 electrons • Total of 10 electrons (1020Ne) • 2nd row of Periodic Table • 8 elements

  39. Periodic Table of Elements • Number of elements in a row is not chance; reflects the maximum number of electrons in the outermost shell • Row 1 < 2 • Row 2 < 8 (plus Row 1) • Row 3 < 8 (plus Row 1 + Row 2) ) • Row 4 < 18 (plus Row 1 + Row2 + Row 3) • Etc.

  40. Periodic Table as a “Model” • Models = conceptual and/or mathematical expressions that help scientists understand how the natural world operates • Models foster predictions about how the natural world operate • Model of the structure of the atom predicts … • Your model of your family dynamic predicts … • Periodic table predicts that unknown “elements” have specific physical and chemical properties

  41. Predictive Value of the Periodic Table ? ?

  42. Question In the Periodic Table, neon is element # 10. How many electrons does neon have in its outermost electron shell? A. 2 B. 4 C. 6 D. 8

  43. Topics • Discovery of atomic structure and function • Models of atoms • Thompson and Rutherford atom (~1900) • Bohr atom (1913) • Quantum mechanics (1930’s) • Elements, atoms and the Periodic Table • Electrons in orbits nested within shells • Valence electrons

  44. Atoms, Elements and Quantum Mechanics01 and 06 October 2015 Physics Chemistry Astronomy Geology/Ecology Biology

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