c=lu Name Some Characteristics of Light So What Is Light? Overview

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1 Chp 6: Atomic Structure 1. Eectromagnetic Radiation 2. Light Energy 3. Line Spectra & the Bohr Mode 4. Eectron & Wave-Partice Duaity 5. Quantum Chemistry & Wave Mechanics 6. Atomic Orbitas Overview Chemica Reactions are a Resut of Eectron Interactions Between Various Eements Eementa Behavior Is the Resut of the Eement s Eectronic Structure Periodic Tabe is Based on an Eements Eectronic Structure 1. Absorption - An Eectron Absorbs the Light, Acquiring It s Energy and Entering an Excited State 2. Emission - An Eectron Reaxes to a Lower Energy State Whie Emitting Light Name Some Characteristics of Light 1. Light Traves Through Space 2. Light has Coor 3. Light has Energy 4. Light Energy is Quantized So What Is Light? 6.1 Eectromagnetic Radiation Waveength () - Distance Between two Peaks Frequency (u) - How Often Waves Goes Through a Compete Cyce (1/sec = hertz) Speed (c) - How Fast Wave Propagates c = 3 X 10 8 m/sec c=u Spectrum c u u c 1

2 6.2 Nature of Matter: Wave- Partice Duaity Light exhibits both wave and partice behavior. Photon - Partice of Light E = nhn, where n = # of photons Einstein s Photoeectric Effect (Einstein) Eectromagnetic Radiation & Energy Panks Constant reates the Energy of a photon of ight to it s frequency. E=hu h=panck s Constant h= 6.63X10-34 J. sec How do we reate the Energy of ight to it s waveength? from c u c E h Eectromagnetic Radiation & Energy Sma Waveength High Frequency High Energy E=hu Large Waveength Low Frequency Low Energy Light Intensity I = nhu (n = moes of photons) Think about the video on Einstein s photoeectric effect and the difference between intense red ight and weak bue ight Waveength (meters) Photon Energy Probem How many photons of microwave radiation ( =125mm) are required to heat 1 L of water from 20.0 o C to the boiing point? E Light = q nhu = msdt -Use s for specific heat capacity as c is the speed of ight Sodium Line Spectra Sodium gives off yeow ight of a specific waveength of nm. What is the frequency of the yeow ine spectra of sodium? 2

3 Sodium Line Spectra Sodium gives off yeow ight of a specific waveength of nm. 1. Determine E for a photon of sodium yeow ight Bohr Mode of Hydrogen Atom Correcty Described the Hydrogen Spectrum Used Concept of Orbits (Wrong) Used Concept of Quantized Energy Leves (Right) 2. Determine E for a moe of photons of sodium yeow ight Bohr Equation for Hydrogen Energy of the nth eve: R H = Rydberg constant R H =Rhc E n R H = 2.18x10-18 J Energy for transition n i --> n f : R H 1 ( ) 2 n 1 1 DEn ( ) i n E f n E f n hu R i h n n DE hu R ni n f 1 1 ) 2 n n h( 2 i f 2 2 f i n f = 1 for UV ight Bohr Mode of Hydrogen Atom n f = 2 for visibe ight n f = 3 for IR ight Bohr Probem: What Is the Energy Leve of the Excited State Which Is Responsibe for the Bue Green Emission Line at nm? That is, what is the initia quantum state; n i? Emission is an exothermic process Absorption is an endothermic process 6.4 Wave-Partice Duaity De Brogie s Hypothesis: A Matter has a Characteristic Waveength 2 hc E mc hv h mv v=veocity & mv = momentum Note the inverse reationship between the mass and the waveength 3

4 DeBrogie Waveength of Eectron Cacuate the DeBrogie Waveength of an Eectron moving at 1.00% the speed of ight c = 3x10 8 m/s, m=9.11x10-31 kg E = mc 2 E = hu c=u mc 2 = hu u c mv = h mc 2 = hc mc = h DeBrogie Waveength of Eectron Cacuate the DeBrogie Waveength of an Eectron moving at 1.00% the speed of ight c = 3x10 8 m/s, m=9.11x10-31 kg Wave-Partice Duaity Eectron Diffraction eec = 2.4 x m and is diffracted by a crysta ike NaC Wave-Partice Duaity - Uncertainty The characteristic waveength of an eectron in a hydrogen atom is 240pm The size of an isoated H atom is about 240 pm This eads to an uncertainty in the ocation of the eectron Heisenberg s Uncertainty Principe You can not simutaneousy know both the position and momentum of an eectron To measure the position of an eectron, you need a waveength smaer than it s characteristic waveength, which is of such a high energy that it aters the eectron s position during the measurement process Physica Meanings of Wave Functions Bohr Mode Uses Orbits Quantum Mechanics Uses Orbitas (Y 2 ) Y 2 - Probabiity Distribution Function, Describes the probabiity of finding an eectron in a specific ocation for a given energy state 4

5 Physica Meanings of Wave Functions Bohr Mode Uses Orbits Quantum Mechanics Uses Orbitas (Y 2 ) Orbitas are Probabiity Distribution Functions - They Represent the Probabiity of Finding an Eectron at a Certain Space in Time Different Orbitas Are Defined by Their Shapes and Distance From the Nuceus Quantum Numbers Bohr Orbits Can Be Described by One Quantum Number, N, the Principe Quantum Number Quantum Mechanics Uses 4 Quantum Numbers n - Principe Quantum Number - Azimutha Quantum Number m - Magnetic Quantum Number m s - Spin Quantum Number (Dirac) Quantum Numbers Each Orbita Can Be Described by It s Set of Quantum Numbers No Two Eectrons Can Have the Same Set of Quantum Numbers n - Principe Quantum Number n has integra vaues; n = 1,2,3... n correates to the shes and the periods of the periodic tabe There are n 2 orbitas in each she The Larger the Vaue of n, the Greater the Average Distance From the Nuceus & the Greater the Orbita s Energy - Azmutha Quantum Number Describes the shape of the orbita Use etters to designate vaues of s: =0 p: =1 d: =2 f: =3 has vaues of 0 to n-1 for each principe eve -The 1st Principe Leve has = 0 - the 2nd has = 0,1 - the 3rd has = 0,1,2 - the 4th has = 0,1,2,3 - a the rest have 4 or ess 1s 2s, 2p 3s, 3p, 3d 4s, 4p, 4d, 4f m - Magnetic Quantum Number Describes Orientation in Space There are 2+1 vaues of m for each type of azmutha quantum number with vaues ranging form to - 1 type of s ( = 0) orbita 3 types of p ( = 1) orbitas 5 types of d ( = 2) orbitas 7 types of f (=3) orbitas 5

6 Each Orbita can be identified by it s Quantum numbers n Exampe, 2p x, use etters s,p,d & f m, describes orientation 6.6 Orbita Shapes & Energies: S Orbitas (=0) Spherica in Nature Baoon Diagram shows region of 90% probabiity of finding eectron A Periods Have S Orbitas 1s 2s 3s Onion Skin ayers of 1st 3 S orbitas Y 2 s orbita radia probabiity functions 1s Y 2 2s Y 2 3s P Orbitas (=1) There are 3 types of P orbitas 2 nd Period & Greater Have P Orbitas node nodes r r r d Orbitas (=2) 5 types of d orbitas 3 rd Period & Greater Have d Orbitas f orbitas 7 types of f orbitas 4 th Period & Greater Have f Orbitas 6