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NCSU CH 101 - Chemisty Chapter 2 Notes

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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 and a particleo Light waves vary inwavelength and frequencieso Includes radio waves,microwaves, UV, X-raysand 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 wavelengthC = νλo 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 - Planck’s Constanto The energy of light is proportional to it’s frequency E = hvo Planck’s Constant is h which is equal to 6.626*10-34o 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 frequencyo 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 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- Centripital Forceo Electrons are kept in orbit by the Coulombic attraction of the nucleuso Angular momentum isproportional to the principalquantum number, n cannotequal 0o The Bohr Radius r1= 52.92pm Potential energy of the electron arises from it’s Coloumbic energy interation with thenucleus and it’s kinetic energyo Total energy of an election in the nthobrit: En = ½Un = ½(kqeqN/εrn)- 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)- 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 - Enloo A photon must be absorbed if the energy of the electron increaseso It must be emitted if the energy decreaseso 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 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- Electrons and Waveso Electrons also behave as both a wave and a particleo Wavelength relationship is represented through the wave equationL = 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 more orbitals, dictates shape and orientationm ≠ 0; -l < ml <+lo ms – spin quantum numberonly 2 availible options+1/2 or -1/2 are the two electron spin directions-Characteristicso The physical characteristics of each spectral linesharp, principal, diffuse, or fundamentalo Quantum numbers dictate the number of orbitals in a sublevelo Electron spin is a quantum mechanical effectn cannot be 0; l cannot equal n; m cannot be greater than l; m must lie between positive and negative lVI. Orbital Shapes, Sings & Sizes- ElectronsoVII. Electron ConfigurationsVIII.Quantum Theory & The Periodic


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