NCSU CH 101 - Chemisty Chapter 2 Notes (8 pages)

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Chemisty Chapter 2 Notes



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Chemisty Chapter 2 Notes

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8
School:
North Carolina State University
Course:
Ch 101 - Chemistry - a Molecular Science
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Chemisty Chapter 2 Notes I Nature of Light Electromagnetic Radiation o Oscillating electric and magnetic fields that travel though space at a speed of 2 998x108 m s o Light behaves as both a wave and a particle o Light waves vary in wavelength and frequencies o Includes radio waves microwaves UV X rays and Yrays Light Properties o Wavelength Distance between 2 maxima minima o White light Sum of all of the colors that comprise visible light o Frequency the number of oscillations of a light wave during one second measured in nm o Relationship between speed frequency and wavelength C C Speed of light 3 00 108 m s V Frequency Wavelength o Long wavelength small frequency low energy o Short wavelength large frequency high energy o The Light Spectrum is a display of the component colors of a light beam seperated by wavelengths o Because all colors continuously merge together they form a continuous spectrum II Quantization Discovery o The energy of a system at the atomic level could not take on continuous values the are quantized or discrete o All object emit electromagnetic waves which increase with temperature o This emission from a warm body is called blackbody radiation o The total energy of a wave cannot be varied continuously because it s composed of a lot of tiny bundle of energy called quanta Max Planck o Solved the Ultraviolet Catastrophe Why metal glowed white instead of staying red when hot Found that objects can gain or lose energy by absorbing emitting energy by absorbing emitting radiant energy in quanta Planck s Constant o The energy of light is proportional to it s frequency E hv o Planck s Constant h is equal to 6 626 10 34 o Light consists of particles called photons which posses discrete energy o Energy in a wave is E nhv n number of quanta in the wave o Increasing the intensity of light increases the number of quanta it contains Photoelectric Effect o When certain metals are irradiated wih light they eject electrons o o o with kinetic energy There is a minimum frequency below which no electrons are ejected called the threshold frequency One photon with enough energy can dispace an electron When frequency of light threshold frequency Energy of quantum W Excess energy is converted into the kinetic energy of the ejected electron KE hv W hv hvo No electrons are observed until light of a certain minimum energy is used but above that energy threshold the number of electrons ejected depends on light intensity not light energy The stream of quanta were later named photons Energy of each photon hv Beam that contains n photons has total energy nhv o Wave Particle Duality o Light behaves as both a particle and a wave o Spectrum a plot of how much light is absorbed or emitted versus the wavelength or frequency Atomic spectra help determine the composition of mixtures and elements present The study of them is called spectroscopy o We can separate light into lines to produce a line spectrum Each line of these represents on the component colors of the observed light There are 40 spectral lines for hydrogen atoms o Rydberg Equation nhi nlo are integers RH 3 290 1015s 1 III Bohr Model In Class Discussion o Bohr disproved the classical view Came up with Quantum Mechanics Electrons can only exist Centripital Force o Electrons are kept in orbit by the Coulombic attraction of the nucleus o Angular momentum is proportional to the principal quantum number n cannot equal 0 o Electrons can only exist in orbitals o The Bohr Radius r1 52 92pm Potential energy of the electron arises from it s Coloumbic energy interation with the nucleus and it s kinetic energy o Total energy of an election in the nth obrit o Total energy expressed in terms of n Basic Charge o Basic unit of charge q 1 602 10 19 o Qe q charge on an electron o QN Zq 1 Charge on a nucleus with Z protons Atomic Line Emission Spectra o Excited atoms emit light of only certain wavelengths that are specific to that element o Balmer Series Hydrogen atom spectrum 4 specified quantized energy units Energy Levels o Energy of an electron in an atom is quantized they get closer with increasing n value o Atomic spectra move on energy level to another through electronic transition If nhi is the higher quantum and nlo is the higher quantum the difference between the two energy levels is E Enhi Enlo o Find the energy of o A photon must be absorbed if the energy of the electron increases o It must be emitted if the energy decreases o Lowest energy line 3 2 Highest energy 6 2 High energy electrons collide with atoms and transfers some of its energy to an electron in the atom they then give up the initially absorbed energy o Light is a form of energy that results from changes that occur during atomic and molecular processes Visible light originates in electronic transition all color is the result of these transitions IV Quantum Theory Wave Mechanics o Bohr observed Quantized Energy States o Schrodinger discovered Theoretical Wave Models De Broglie proposed that all movig objects have wave properties o De Broglie discovered Wave Mechanics Since E MC2 and E hv hc He concluded that MC2 hc Electrons form standing waves around the nucleus Schrodinger applied electrons behaving as waves to the problems of electrons in atoms Came up with math relationships for Balmer s series Electrons and Waves o Electrons also behave as both a wave and a particle o Wavelength relationship is represented through the wave equation L n 2 integer n must be positive and nonzero o Points where waves have no amplitude are called nodes o Wave Particle Duality applies to electrons as well o Uncertainty Principle the precise position and velocity of an electron cannot be known V Future positions and velocities can t be predicted Quantum Numbers Wave Equations o Erwin Schrodinger came up with the wave equation which can be o solved to produce wave functions Quantum Numbers n the principle quantum number l angular momentum quantum number ml magnetic quantum number ms spin quantum number The Quantum Numbers o n the principal quantum number Integer greater than zero designates level indicates energy contains one sublevels one or more orbitals dictates shape and orientation only 2 availible options o l angular momentum quantum number 0 l n o ml magnetic quantum number m 0 l ml l o ms spin quantum number 1 2 or 1 2 are the two electron spin directions Characteristics o The physical characteristics of each spectral line sharp principal diffuse or fundamental o Quantum numbers dictate


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