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Chemistry 281(01) Winter 2017. CTH 227 10:00-11:15 am Instructor: Dr. Upali Siriwardane E-mail : firstname.lastname@example.org 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 . Tests
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Chemistry 281(01) Winter 2017 CTH 227 10:00-11:15 am Instructor: Dr. UpaliSiriwardane E-mail: email@example.com 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. Tests January 12, 2017 Test 1 (Chapters 1&,2), February 2, 2017 Test 2 (Chapters 3 &4) February 22, 2017, Test 3 (Chapters 5 & 6), Comprehensive Final Make Up Exam: February 23, 2017 10:00-11:15 AM, CTH 227.
Chapter 1. Atomic Sturcture • Chapter 1. Atomic structure 3 • The origin of the elements 3 • The nucleosynthesis of light elements 4 • The nucleosynthesis of heavy elements 4 • The structures of hydrogenic atoms 10 • 1.1 Spectroscopic information 10 • 1.2 Some principles of quantum mechanics 11 • 1.3 Atomic orbitals 12 • Many-electron atoms 18 • 1.4 Penetration and shielding 18 • 1.5 The building-up principle 17 • 1.6 Classification of elements 20 • 1.7 Atomic parameters22
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 entity consisting of only Hydrogen and Helium during it's incipient stages.
Sun & Planet formation in the Universe Over the expanse of many years, and through star formations and a continuing process of fusion and fission, our universe has come to consist of numerous chemical elements, four terrestrial planets (Venus, Mercury, Earth, and Mars), and five giant gas planets (Jupiter, Saturn, Uranus ,Neptune, and Pluto).
The origin of the elements • Basic concepts of nuclear chemistry and nucleosynthesis • The nucleosynthesis of light elements • The nucleosynthesis of heavy elements • Abundances of elements earth’s crust, • sun and the universe • The structures of hydrogenicatoms
Nuclear Chemistry • Fusion is lighternuclei coming together to form heavier. • Fission is heavier nuclei breaking in to lighter nuclei. • There is a Mass Defect, 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 amu multiplied by the conversion factor (931.5 MeV/amu) • Binding energy of nuclei expressed in Mev/nucleons
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
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
Radio Activity and Nuclear Kinetics • Nuclear reactions? • Fusion • Fission • What kinetics fission follow?
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
Kinetics Definitions and Concepts a) The Rate of a Nuclear Reaction b) rate law b) rate (decay) constant c) order (Nuclear reactions are always 1st order) d) differential rate law c) integral rate law d) Half-life law
1 [A]0 Graphical method [A]t [A]0 1 [A]t 1 [A]t
Nt N0 Nt N0 Important Nuclear Reaction Equations
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
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.
The nucleo-synthesis of elements Stellar nucleo-synthesis Lighter Elements (up to 56) Elements carbon to Iron is form by nuclear fusion in stars after all H is converted to He. Most of the lighter elements up to iron in the universe are formed by fusion of lighter elements. Heavy elements (above 56) Most of the heavier elements up to trans uranium in the universe are formed during supernova explosions by neutron capture of iron followed by fission.
Supernova Explosion Giant one star supernova explosions A heavier star buns all its H and nuclear fusion 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. Corpse of supernova explosion leaves a core neutrons. Iron capture neutrons and all heavier elements beyond iron.
Stability of the Elements and Their Isotopes P/N Ratio Why are elements With Z > 82 are Unstable?
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.
Spectroscopic Information 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.
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.
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.
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 = -
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
( ) 1 ni2 1 nf2 - Bohr model of the atom Balmer later determined an empirical relationship that described the spectral lines for hydrogen. En = - From Quantum Mechanics 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.
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.
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
Particle nature of 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
Properties of Waves • Wavelength • Frequency • Speed • Amplitude • Constructive Interference • Destructive interference • Reflection • Refraction • Diffraction of waves
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
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.
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