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Chemistry 281(01) Winter 2014

Chemistry 281(01) Winter 2014. CTH 277 10:00-11:15 am Instructor: Dr. Upali Siriwardane E-mail :  upali@latech.edu Office:  311 Carson Taylor Hall ; Phone: 318-257-4941; Office Hours:  MTW 8:00 am - 10:00 am; TR 8:30 - 9:30 am & 1:00-2:00 pm.

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Chemistry 281(01) Winter 2014

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  1. Chemistry 281(01) Winter 2014 CTH 27710:00-11:15 am Instructor: Dr. UpaliSiriwardane E-mail:  upali@latech.edu Office:  311 Carson Taylor Hall ; Phone: 318-257-4941; Office Hours:  MTW 8:00 am - 10:00 am; TR 8:30 - 9:30 am & 1:00-2:00 pm. January 14, 2014 Test 1 (Chapters 1&,2), February 6, 2014 Test 2 (Chapters 3 &4) February 25, 2014, Test 3 (Chapters 5 & 6), Comprehensive Final Make Up Exam: February 27, 2012 9:30-10:45 AM, CTH 311.

  2. Chapter 1. Atomic Sturcture Chapter 1.  Atomic structure                                           3    The origin of the elements                                              3 1.1 The nucleosynthesis of light elements                       5 1.2 The nucleosynthesis of heavy elements                   6 1.3 The classification of the elements                                8     The structures of hydrogenic atoms                           10 1.4 Spectroscopic information                                           10 1.5 Some principles of quantum mechanics                      11 1.6 Atomic orbitals                                                            12     Many-electron atoms                                                    18 1.7 Penetration and shielding                                             18 1.8 The building-up principle                                             20 1.9 Atomic parameters

  3. Origin of Elements in the Universe Scientists have long based the origin of our Universe on the Big Bang Theory. According to this theory, our universe was simply an expanding fairly cold entity consisting of only Hydrogen and Helium during it's incipient stages. Over the expanse of many years, and through a continuing process of fusion and fission, our universe has come to consist of numerous chemical elements, four terrestrial planets (Earth, Mars, Venus, and Mercury), and five giant gas planets (Saturn, Jupiter, Neptune, Pluto, and Uranus).

  4. Eight Steps in the History of the Earth 1. The Big Bang 2. Star Formation 3. Supernova Explosion 4. Solar Nebula Condenses 5. Sun & Planetary Rings Form 6. Earth Forms 7. Earth's Core Forms  8. Oceans & Atmosphere Forms

  5. Nuclear Chemistry • Fusion is lighter nuclei coming together to form heavier. • Fission is heavier nuclei breaking in to lighter nuclei. • Mass is not conserved E=mc2 • Nuclear reactions are balanced by A (mass) and Z (atomic) number. • Energy released is E=mc2, m is mass defect in amumutiplied by the conversion factor (931.5 MeV/amu) • Binding energy of nuclei expressed in Mev/nucleons

  6. Balancing Nuclear Equations

  7. Nuclear Binding Energy The binding energy of a nucleus is a measure of how tightly its protons and neutrons are held together by the nuclear forces. The binding energy per nucleon, the energy required to remove one neutron or proton from a nucleus, is a function of the mass number A. (Dm) –mass defect (Dm) = Mass of Nuclide - mass of (p + n +e ) Proton mass: 1.00728 amu Neutron mass: 1.00867 amu 931.5 MeV/amu Electron mass: 0.00055 amu Mass defect (Dm), then multiply by

  8. Bonding Energy Curve

  9. Nuclear Fusion Reactions • Nuclear energy, measured in millions of electron volts (MeV), is released by the fusion of two light nuclei, as when two heavy hydrogen nuclei, deuterons (2H), combine in the reaction

  10. Nuclear Fission Reactions • Nuclear energy is also released when the fission (breaking up of ) of a heavy nucleus such as U is induced by the absorption of a neutron as in

  11. Origin of the Elements: Nucleosynthesis • Elements formed in the universe's original stars were made from hydrogen gas condensing due to gravity. These young stars "burned" hydrogen in fusion reactions to produce helium and the hydrogen was depleted. Reactions such as those below built up all the heavier elements up to mass number 56 in the periodic table. • When the stars got old they exploded in a super nova, spreading the new elements into space with high flux of neutrons to produce heavy elements by neutron capture.

  12. Nuclear Burning

  13. Supernova Explosion

  14. The nucleo-synthesis of light elements • Stellar nucleo-synthesis Elements carbon to Iron is form by nuclear fusion in stars after all H is converted to He. • Double star Supernova White dwarf (dense ball of carbon/oxygen) steals material from another star and get heated releasing huge energy. It goes to nuclear overload and carbon/oxygen suddenly fuses to iron and it explodes known as type 1a supernova. Most of the elements up to iron in the universe

  15. The nucleosynthesis of heavy elements Havier elements are formed during Supernova explosion. Giant one star supernova explosions A heavier star buns all its H and nuclear burning goes faster and forms layer after layers of new elements with increasing mass number up to iron. Core collapses and become denser and the star explodes. Iron capture neutrons and all heavier elements beyond iron. Corpse of supernova explosion leaves a core neutrons. Rotating neutron produces EM pluses creating a pulsar Hypernova explosions: g-ray bursts

  16. Cosmic Abundances

  17. Terrestrial Abundances

  18. Stability of the Elements and Their Isotopes P/N Ratio Why are elements With Z > 82 are Unstable?

  19. Terrestrial Abundances

  20. Magic Numbers • Nuclei with either numbers of protons or neutrons equal to Z, N =2 (He), 8(O), 20 (Ca), 28(Si), 50(Sn, 82(Pb), or 126(?)(I) • exhibit certain properties which are analogous to closed shell properties in atoms, including • anomalously low masses, high natural abundances and high energy first excited states.

  21. The classification of the elements • Dobereiner Triads • Newlands called the Law of Octaves • Mendeleyev’s periodic table • LotharMeyer’s atomic volume curves • Glen Seaborg atomic number and long form

  22. Dobereiner Triads

  23. Newlands’ Law of octaves

  24. Lothar Mayer’s atomic volume curves

  25. Mendeleyev’s Periodic Table

  26. Long Form of Periodic Table

  27. What is periodic table? Describe its use in chemistry? All elements in a group have similar chemical properties Group I- alkali metal:Li, Na, K Rb, Cs, Fr Common ele.nconn: ns1 Group II- alkaline earth metals:Be, Mg, Ca, Sr, Ba, Ra: Common ele.nconn: ns2 Group VII- Halogens: Cl, Br, I, At: Common ele.n conn:ns2 np5 Group VIII- Noble gases:He, Ne, Ar, Kr, Xe, Rn: Common ele.nconn ns2 np6

  28. Chemical properties and the periodic table Electron configurations help us understand changes in atomic radii, ionization energies, and electron affinities. Various trends in reactivity can be observed. • Main group metals become more reactive as you go down a group. • Reactivity of nonmetals decreases as you go down a group. • Transition metals become less reactive as you go down a group.

  29. Other ways of numbering groupsin the periodic table • Several methods are used for numbering periodic table groups • American chemists preferred method. • The IUPAC old system. • The IUPAC current system. • The American Chemical Society (ACS) has also adopted the current IUPAC system.

  30. IA IIA III B IVB VB VIB VIIB VIIIB 1 213 14 15 16 17 18 IA IIA IIIA IIIA IVA VA VIA VIIA 0 H He 1 2 3 4 Li Be B C N O F Ne IIIA IVA VA VIA VIIA VIIIA IB IIB 3 4 5 6 7 8 9 10 11 12 Na Mg Al Si P S Cl Ar IIIB IVB V B VIB VIIB VIII B IB IIB K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Other numbering systems Previous IUPAC Current IUPAC and ACS Preferred US

  31. The structures of hydrogenic atoms :Bohr Theory • The Bohr model is a ‘planetary’ type model. • Each principal quantum represents a new ‘orbit’ or layer. • The nucleus is at the center of the model.

  32. Emission Spectrum of Hydrogen • Bohr studied the spectra produced when atoms were excited in a gas discharge tube. He observed that each element produced its own set of characteristic lines.

  33. Emission Spectrum of Hydrogen • Line Spectrum • Energy is absorbed when an electron goes from a lower(n) to a higher(n) • Energy is emitted when an electron goes from a higher(n) to a lower(n) level • Energy changed is given by:DE = Ef - Ei • or DE = -2.178 x 10-18 [1/n2f - 1/n2i] J • DE is negative for an emission and positive for an absorption • DE can be converted to l or 1/ lby l = hc/E.

  34. Bohr model of the atom • The Bohr model is a ‘planetary’ type model. • Each principal quantum represents a new ‘orbit’ or layer. • The nucleus is at the center of the model. • RH = 2.178 x 10-18 J En = RH En = -

  35. What is Bohr’s Atomic model? • explain emission spectrum of hydrogen atom • applied the idea of Quantization to electrons to orbits • energies of these orbits increase with the distance from nucleus. • Energy of the electron in orbit n (En): • En = -2.178 x 10-18 J (Z2/n2) • En = -2.178 x 10-18 J 1/n2; Z=1 for H

  36. ( ) 1 ni2 1 nf2 - Bohr model of the atom Balmer later determined an empirical relationship that described the spectral lines for hydrogen. En = - DE = - 2.178 x 10-18J nf = 2 ni = 3,4, 5, . . . Blamer series Spectra of many other atoms can be described by similar relationships.

  37. Paschen, Blamer and Lyman Series

  38. Calculation using the equation: E = -2.178 x 10-18 (1/nf2 - 1/ni2 ) J, Calculate the wavelength of light that can excite the electron in a ground state hydrogen atom to n = 7 energy level.

  39. Calculation using Bohr eqaution The energy for the transition from n = 1 to n = 7: DE = -2.178 x 10-18 J [1/n2f - 1/n2i]; nf = 7, ni = 1 DE = -2.178 x 10-18 [1/72 - 1/12] J DE = -2.178 x 10-18 [1/49 - 1/1] J DE = -2.178 x 10-18 [0.02041 - 1] J DE = -2.178 x 10-18 [-0.97959] J = 2.134 x 10-18 J (+, absorption) calculate the l using l = hc/E 6.626 x 10-34 Js x 3.00 x 108 m/s l = ---------------------- 2.13 x 10-18 J l = 9.31 x 10-8 m

  40. Wave- Particle Duality of Matter and Energy • Wave theory applies to electromagnetic radiation • EMR can also be described as particles • quanta :A particles of light energy. • Quantum: One particle of light with a certain energy. • Photon: A stream of Quanta • Wave theory could be applied to electrons

  41. Wave theory of the electron • 1924:De Broglie suggested that electrons have wave properties to account for why their energy was quantized. • He reasoned that the electron in the hydrogen atom was fixed in the space around the nucleus. • He felt that the electron would best be represented as a standing wave. • As a standing wave, each electron’s path must equal a whole number times the wavelength.

  42. h mv l = De Broglie waves De Broglie proposed that all particles have a wavelength as related by: l = wavelength, meters h = Plank’s constant m = mass, kg v = frequency, m/s

  43. Wave Character of Electrons

  44. What is a wave-mechanical model? • motions of a vibrating string shows one dimensional motion. • Energy of the vibrating string is quantized • Energy of the waves increased with the nodes. • Nodes are places were string is stationary. • Number of nodes gives the quantum number. One dimensional motion gives one quantum number. Vibrating String : y = sin(npx/l) d2y/dx2 = -(n2p2/l2)sin(npx/l) = -(n2p2/l2)y

  45. Constructively Interfered 2D-Wave

  46. destructively Interfered 2D-Wave

  47. Two-dimensional wave - Vibrations on a Drumskin One circular node (at the drumskin's edge) Two circular nodes (one at the drumskin's edge plus one more) Three circular nodes (one at the drumskin's edge plus two more) One transverse node (plus a circular one at the drumskin's edge) Two transverse nodes (plus one at the drumskin's edge)

  48. How did Schrodinger come up with a equation started with The “Vibrating String” and the "Particle in a One-dimensional Box“ solutions Vibrating String : y = sin(npx/l) d2y/dx2 = -(n2p2/l2)sin(npx/l) = -(n2p2/l2)y Since l = 2l/n; d2y/dx2 = -(4m2v2/h2)y 1/l2= 4/ l2n2; l = h/mv; 1/l2= 4/l2n2 = 4m2v2/h2 Particle in an One-dimensional Box: d2y/dx2 = -(4m2v2p2/h2)y E = ½mv2 + V or v2 = (2/m)(E-V) d2y/dx2 = -(8mp2/h2)(E - V)y

  49. Schrödinger Equation  = wave function E = total energy V = potential energy

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