I. Nature of LightChemisty Chapter 2 NotesI. Nature of Light- Electromagnetic Radiationo Oscillating electric and magnetic fields that travel though space at a speed of 2.998x108 m/so Light behaves as both a wave anda particleo Light waves vary in wavelengthand frequencieso Includes radio waves,microwaves, UV, X-rays and Y-rays- Light Propertieso Wavelength (λ): Distance between 2 maxima & minimao White light: Sum of all of the colors that comprise visible lighto Frequency: the number of oscillations of a light wave during one second (measured in nm)o Relationship between speed, frequency, and wavelengthC = νλ- C = Speed of light (3.00*108 m/s)- V= Frequency- λ= Wavelengtho Long wavelength small frequency low energyo Short wavelength large frequency high energyo The Light Spectrum is a display of the component colors of a light beam, seperated by wavelengthso Because all colors continuously merge together, they form a continuous spectrumII. Quantization- Discoveryo 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 temperatureo This emission from a warm body is called blackbody radiationo 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 Plancko 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 Constanto The energy of light is proportional to it’s frequency E = hvo Planck’s Constant: h is equal to 6.626*10-34o Light consists of particles called photons which posses discrete energyo 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 Effecto When certain metals are irradiated wih light, they eject electrons 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 electrono 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 - hvoo 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 energyo The stream of quanta were later named photons Energy of each photon = hvo Beam that contains n photons has total energy = nhv- Wave-Particle Dualityo Light behaves as both a particle and a waveo 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 spectroscopyo 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 atomso Rydberg Equation nhi > nlo are integers RH = 3.290*1015s-1III. Bohr Model- In Class Discussiono Bohr disproved the classical view Came up with Quantum Mechanics Electrons can only exist - Centripital Forceo Electrons are kept in orbit by the Coulombic attraction of the nucleuso Angular momentum isproportional to the principalquantum number, n cannotequal 0o Electrons can only exist in orbitalso 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 energyo Total energy of anelection in the nthobrit:o Total energyexpressed interms of n:- Basic Chargeo Basic unit of charge = q = 1.602*10-19o Qe= -q (charge on an electron)o QN= +Zq. ε=1 (Charge on a nucleus with Z protons)- Atomic Line Emission Spectrao Excited atoms emit light of only certain wavelengths that are specific to that elemento Balmer Series: Hydrogen atom spectrum 4 specified quantized energy units- Energy Levelso Energy of an electron in an atom is quantized, they get closer with increasing n valueo 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: - ΔE = Enhi - EnlooFind the energy of o A photon must be absorbed if the energy of the electron increaseso It must be emitted if the energy decreaseso Lowest energy line: (32); Highest energy (62) High energy electrons collide with atoms and transfers some of its energy to an electron in the atom, they then giveup the initially absorbed energyo 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 transitionsIV. Quantum Theory- Wave Mechanicso Bohr observed Quantized Energy States De Broglie discovered Wave Mechanics- Schrodinger discovered Theoretical Wave Modelso De Broglie proposed that all movig objects have wave properties Since E=MC2, and E=hv=hc/λ He concluded that MC2= hc/λ- Electrons form standing waves around the nucleuso Schrodinger applied electrons behaving as waves to the problems of electrons in atoms Came up with math relationships for Balmer’s series- Electrons and Waveso Electrons also behave as both a wave and a particleo Wavelength relationship is represented through the wave equationL = n(λ/2) - integer n must be positive and nonzeroo Points where waves have no amplitude are called nodes o Wave-Particle Duality applies to electrons as wello Uncertainty Principle: the precise position and velocity of an electron cannot be known.Future positions and velocities can’t be predictedV. Quantum Numbers- Wave Equationso Erwin Schrodinger came up with the wave equation which can be solved to produce wave functionso Quantum Numbers n – the principle quantum number l – angular momentum quantum number ml – magnetic quantum number ms – spin quantum number- The Quantum Numberso n – the principal quantum number Integer greater than zero, designates level, indicates energyo l – angular momentum quantum number contains one+ sublevels 0 < l < no ml – magnetic quantum number one or
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