Atomic Structure and Function: Outline

1. Atomic Structure and Function:Outline • Early history in 18th and 19th centuries • Discovery of elements and the Periodic Table (1869) • Discovery of the electron (1897) • Discovery of the nucleus (1911) • Atomic structure with consternation • Atomic structure: the Bohr atom (1913) • Atomic Structure: Theory of Quantum Mechanics (1930’s) • Applications of our understanding

2. Atomic Structure and Function:Take Home Message • Science as a evolutionary, incremental process over decades (e.g., exploring the structure of atom) • Role of hypothesis development and testing in the sciences • Demystification of physics and chemistry: structure of the atom is a simple concept • Understanding of atomic structure underpins future course topics (e.g., geology, biochemistry, environmental sciences, binding of chemicals) • Applications – some examples

3. Early History in 18th and 19th Century • Atomic Theory of Dalton • Atoms • Elements • Molecules/compounds (e.g., water or H2O) • Atoms as basis for understanding chemistry but without electrons, protons and neutrons (analogy to a marble)

4. Early History in 18th/19th Century:Discovery of Elements • 30 elements known in early 1800’s • Mendeleev and the Periodic Table (1869) • 63 elements known w/o any organization • Ordering of elements • Mass from low to high • Chemical property by column (all behave similarly in a chemical sense); examples • Column I: react with chlorine (1:1 ratio) • Hydrogen (H), Lithium (Li), Sodium (Na), Potassium (K) • Column VII: react with chlorine in (2:1 ratio) • Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr)

5. Draft of Mendeleev’s Table of Elements

6. Mendeleev’s Contribution • Arrange elements from light to heavy • Arranged elements by chemical behavior • Spatial ordering via rows and columns • Product: Periodic Table of Elements • Predictive tool • Immensely creative insight (informatics) • Example of missing elements and predictive capability of Table

7. Atomic Structure and Function:Outline • Early history in 18th and 19th centuries • Discovery of the electron (1897) • Discovery of the nucleus (1911) • Atomic structure with consternation • Atomic structure: the Bohr atom (1913) • Atomic Structure: Theory of Quantum Mechanics (1930’s) • Applications of our understanding

8. Thompson’s Experiment: Discovery of the Electron • Idea that there may be some smaller components that comprise atoms • Hypothesis: Atoms consist of some subcomponents, one of which is negatively charged • Experiment to test hypothesis

9. Atomic Structure and Function:Outline • Early history in 18th and 19th centuries • Discovery of the electron (1897) • Discovery of the nucleus (1911) • Atomic structure with consternation • Atomic structure: the Bohr atom (1913) • Atomic Structure: Theory of Quantum Mechanics (1930’s) • Applications of our understanding

10. Rutherford’s Experiment: Discovery of a Nucleus • Idea that there may be some smaller components that comprise atoms, including negative and positive charges components • Hypothesis: Atoms consist of multiple subcomponents, some negative and some positive • Experiment to test hypothesis • Alpha particles (+), gold foil, “bullets”, and “tracks”

11. Rutherford’s Experiment:

12. Explanation

13. Observations, Hypothesis and Conclusion • Observations: • Almost all alpha’s passed through foil unaffected • Very small number of alpha’s deflected @ small angle • 1/1000 deflected at large angle (struck “head on”) • Hypothesis: Atoms consist of some positive and negative subcomponents • Accept or reject

14. New Model of Atom • Small, dense center, positively charged – called the nucleus (later to be called the proton) • Small, light (w/o mass) negative charged subcomponent circles the nucleus (electron) • Later additions (1932) • Neutrons • Protons • Charge (neutrality calls for + and – charges)

15. Atomic Structure and Function:Outline • Early history in 18th and 19th centuries • Discovery of the electron (1897) • Discovery of the nucleus (1911) • Atomic structure with consternation • Atomic structure: the Bohr atom (1913) • Atomic Structure: Theory of Quantum Mechanics (1930’s) • Applications of our understanding

16. Atomic Structure with Consternation Logic of consternation with Rutherford Model • Electrons moving, so must give off energy; • 2nd Law of Thermodynamics • Electrons should collapse • Yet atoms are billions of years old Conclusions: Model violated fundamental laws of physics

17. Atomic Structure and Function:Outline • Early history in 18th and 19th centuries • Discovery of the electron (1897) • Discovery of the nucleus (1911) • Atomic structure with consternation • Atomic structure: the Bohr atom (1913) • Atomic Structure: Theory of Quantum Mechanics (1930’s) • Applications of our understanding

18. Atomic Structure: Bohr Atom • Observations (1913) • Heated hydrogen gas and light is emitted as a discrete wavelength (not continuous spectrum) • Other gases behave the same in producing discrete wavelength, but each gas unique in wavelengths produced

19. Atomic Structure: Bohr Atom • Hypothesis • Electrons circle the nucleus at specific distances from the nucleus in defined orbits • Diagram

20. Atomic Structure: Bohr Atom • Explanation of light in discrete wavelengths • As “excited”/heated electrons drop back from orbit, a packet of energy is lost as a function of distance from the nucleus • Packet of energy is called photon (light)

21. Atomic Structure: Bohr Atom • Key aspects of the Bohr atom • No space between the orbits for electrons to be so “jump” has to be “all or none” – quantum levels of electrons • Excited electrons in outer orbit has 2 options: • Drop down to next lower orbit and emit a packet of energy (light) unique for that distance • Drop back to even lower level (ground state) and emit packet of energy (light) unique for that that distance • Energy release is unique for each element and is a “window” on atomic structure” • Ideas verified two decades later using quantum mechanics

22. Atomic Structure and Function:Outline • Early history in 18th and 19th centuries • Discovery of the electron (1897) • Discovery of the nucleus (1911) • Atomic structure with consternation • Atomic structure: the Bohr atom (1913) • Atomic Structure: Theory of Quantum Mechanics (1930’s) • Applications of our understanding

23. Theory of Quantum Mechanics • Observations • Behavior of electrons in heated hydrogen gas were consistent with Bohr Model (orbits, etc.) • Behavior of other heavier gases could not be explained by Bohr Model • Investigators: • Heisenberg, Shrodinger, etc. • Key: Integrated mechanisms of waves and particles, focusing on “fuzzy electron clouds” • Product: new model of atomic structure and function • “Quantum mechanics”

24. Quantum Mechanics Model • Key Principles • Electron behaves as a wave not a particle • Energy of electron behaves as a “spread-out wave” – not discrete bundle of energy • Description is based on quantum numbers • Distance from nucleus • Energy level and sublevel • Orientation of electrons in space • Direction of electron spin

25. Quantum Mechanics Model: Principle Energy Level • Main energy level of electrons • Distance from nucleus • n = 1 (lowest energy level) • n = 2 • n = 3 • n = 4 (highest energy level) • etc.

26. Quantum Mechanics Model: Sub-energy Levels • Electrons in “fuzzy” probability distribution called an “orbital” • e.g., n = 1 has I sub-energy level/orbital (2 electron orientations) • Electrons in an orbital can only exist in pairs (2) and the pair spin in opposite directions • Pauli Exclusion Principle

27. Quantum Mechanics Model: Electron Configuration • Electrons always adopt most energetically stable energy levels/orbitals consistent with Laws of Thermodynamics and previous conditions (above) • n = 1 with 2 electrons in 1 orbital (s orbital) • n = 2 with 8 electrons in 4 orbitals (p orbitals) • pw has 2 electrons • px has 2 electrons • py has 2 electrons • pz has 2 electrons

28. Atomic Structure and Function:Outline • Early history in 18th and 19th centuries • Discovery of the electron (1897) • Discovery of the nucleus (1911) • Atomic structure with consternation • Atomic structure: the Bohr atom (1913) • Atomic Structure: Theory of Quantum Mechanics (1930’s) • Applications of our understanding

29. Applications of Our Understanding of Atomic Structure • Spectroscopy: quantum differences in light emitted or absorbed result in unique signature for each element (“fingerprint”) • LASER (Light Amplification by Stimulated Emission of Radiation) • Binding of elements to create compounds • Neurotransmitters in the brain • Allergy reactions • Etc……………..

30. Atomic Structure and Function:Take Home Message • Science as a evolutionary, incremental process over decades (e.g., exploring the structure of atom) • Role of hypothesis development and testing in the sciences • Demystification of physics and chemistry: structure of the atom is a simple concept • Understanding of atomic structure underpins future course topics (e.g., geology, biochemistry, environmental sciences, binding of chemicals) • Applications – some examples