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# Midterm#4.pdf CHM 112

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This 8 page Study Guide was uploaded by Barbi Della Polla on Thursday October 8, 2015. The Study Guide belongs to CHM 112 at University of Miami taught by Vanessa Falcao in Spring2015. Since its upload, it has received 84 views. For similar materials see Principles of Chemistry II in Chemistry at University of Miami.

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Date Created: 10/08/15

Midterm 4 Chemistry THE QUANTUMMECHANICAL MODEL OF THE ATOM CHAPTER 7 Explains the manner in which electrons exist and behave in atoms Predict the properties of atoms related to the behavior od the electrons Nature of light 0 Light form of electromagnetic radiation Speed of the light 300 X 108 ms Characterizing Waves Amplitude height of the wave Larger the amplitude brighter the light Wavelength measure of the distance covered by the wave From one crest to another one 0 Frequency number of waves that pass a point in a given period of time cycles Hz 1 s1 The total energy is proportional to the amplitude and the frequency Larger the amplitude more force More frequently the waves strike more force Shorter the wavelength more frequently they pass same V Color determined by its wavelength or frequency More crestes the light will be bright less crest dim light The Electromagnetic Spectrum visible light comprises only a small fraction of all the wavelengths of light Shorter the wavelength highfrequency light has higher energy Interference interaction between waves Constructive interference when waves interact to make a larger wave it is called in phase Destructive interference when waves interact and they cancel each other Out of phase Diffraction traveling waves encounter an obstacle about the same size the bend around it Photoelectric Effect many metals emit electrons when a light shines on their surface The effect of the light energy is being transferred to the electron Wavelength shorter more electrons should be ejected The problem was that a minimum frequency was needed before electrons would be emitted regardless of the intensity called the threshold frequency Highfrequency light from a dim source caused electron emission without any lag time Einstein s Explanation proposed that the light was delivered to the atoms in packets called quanta or photons The energy of a photon of light is directly proportional to its frequency Plank s Constant h 6626 x 1034 s E hv 2 m 7L Ejected Electrons one photon at the threshold frequency gives the electron just enough energy for it to scape the atoms Binding energy cl Irradiated it with a shorter wavelength photon The electron absorbs more energy than is necessary to escape The excess energy becomes kinetic energy of the ejected electron Kinetic energy Ephoton Ebinding KE hv I Spectra when atoms or molecules absorb energy is often released as light energy 0 Emission spectrum the emitted light is passed through a prism a pattern of particular wavelengths of light is seen that is unique to that type of atom or molecule 0 No continuous Used to identify the material Rutherford s Nuclear Model Nucleus essentially the entire mass of the atom Positively charged 0 The electrons move around in the empty space of the atom surrounding the nucleus PROBLEMS Electrons are moving charged particles giving off energy 0 The electrons should lose energy crash into the nucleus and the atoms should collapse But is doesn t Bohr Model of the Atom the above model does not explain what structural changes occur when the atom gains or loses energy 0 Explain how the structure of the atom changes when it undergoes energy transitions 0 The energy of the atom was quantized the amount of energy in the atom was related to the electron s position in the atom Quantized the atom could only have very speci c amounts of energy Electrons travel in orbits that are at a xed distance from the nucleus Stationary states Electrons emit radiation when they jump from an orbit with higher energy down to an orbit with lower energy Wave Behavior of Electrons Broglie Proposed that particles could have wavelike character 0 Predicted that the wavelength of a particle was inversely proportional to its momentum The wave character of electrons is signi cant 2i H V Electron Diffraction beam of electrons would produce an interference patterns the same as waves do Complementary Properties 0 Wave nature interference pattern 0 Particle nature position which slit it is passing through 0 The wave and particle nature of the electron are complementary properties Uncertainty Principle 0 More accurately you know the position of a small particle such as an electron the less you known about its speed and vice versa Ax gtlt mAv 2 47 Electron Energy is complementary to position Schrodinger s nding an electron with a energy KEZZ 12 calculate the probability of mv2 particular amount of location in the atom Equa on at a particular 0 Solutions to it produce many wave functions w 0 A plot of distance versus wzrepresentsanorbital a probability distribution map of a region where the electron is likely to be found Calculations shown that the size shape and orientation in space of an orbital are determined to be three integer terms in the wave functions Called quantum numbers Principal quantum nuber n Angular momentum quantum number I Magnetic quantum number m Principal Quantum Number n Characterizes the energy of the electron in a particular orbital Bohr s N can be an integer 1 The larger the value of n the more energy the orbital has Energies are de ned as being negative Escape 0 The larger the value of n the larger the orbital As n gets larger the amount of energy between orbitals gets smaller gt En 218 gtlt 10 13 1 llquot Angular Momentum Quantum Number I The angular momentum quantum number determines the shape of the orbital I can have integer values from O to n 1 Each value of l is called by a particular letter that designates the shape of the orbital V s spherical p in nity V d 2 in nities f4 in nities Magnetic Quantum Number m Describing an orbital Each set of n I and m describes one Integer that specifies the orientation of the orbital Values are integer from to including zero Sublevel Principal level speci ed by n speci ed by l orbital quot3 M 2 2 Orbitals with the same value of n are in the same principal energy level 350ml Walla Sggmg39sm Principal shell mlfo mlz l o mlz z 1 12 Orbitals with the same values of n and 112 l are said to be in the same sublevel 3 21 25 orbital 2p orbitals Energy Levels and Sublevels W MEWS Number of sublevels within a level Number of orbitals within a sublevel Number of orbitals in a levels n2 n n1 0 15 orbital E ml0 21 Quantum Mechanical Explanation of Atomic Spectra Each wavelength in the spectrum of an atom corresponds to an electron transition between orbitals Electron exited it transitions from an orbital in a lower energy level to an orbital in a higher energy level Electron relaxed it transitions from an orbital in a higher energy level to an orbital in a lower energy level Also a photon of light is released whose energy equals the energy difference between the orbital Electron Transitions To transitions to a higher state the electron must gain the correct amount of energy corresponding to the difference in energy between the nal and initial states Electrons in high energy states are unstable and tend to lose energy and transition to lower energy states Each line in the emission spectrum corresponds to the difference in energy between two energy states Predicting the Spectrum of Hydrogen The wavelengths of lines in the emission spectrum of hydrogen can be predicted by calculating the difference in energy between any two states o For an electron in energy state n there are n 1 energy states it can transition to Therefore it can generate n 1 lines Energy Transitions in Hydrogen The energy of a photon released is equal to the difference in energy between the two levels the electron is jumping between o It can be calculated by subtracting the energy of the initial state from the energy of the nal state 1 E 2 218x10 18J 218x10 18J Eemitted photon T AE phOton n nalzD hC 1 1 18 AE electron E nal state T 1 EphOton 23918X10 Jn 2 n 2 E It I tate nal Initial InI la 5 Probability and Radial Distribution Functions 0 p2 is the probability destiny the prob of nding an electron at a particular point in space decreases as you move away from the nucleus 0 The radial distribution function represents the total probability at a certain distance from the nucleus Nodes in the functions are where the probability drops to 0 Probability Density Function represents the total probability of nding an electron at a particular point in space Radial Distribution Function represents the total probability of nding an electron within a thin spherical shell at a distance r from the nucleus 0 The probability at a point decreases increasing distance from the nucleus but the volume of the spherical shell increases l O the s Orbital Each principal energy level has one s orbital Lowest energy orbital in a principal energy state Sphencal Number of nodes n 1 l 1 p orbitals Each principal energy state above n 1 has three p orbitals M 1 0 1 0 Each of the three orbitals points along a different axis Px Py P2 0 The second lowest energy orbitals in a principal energy state Twolobed One node at the nucleus total 0 n nodes I 2 d Orbitals Each principal energy state above n 2 1 O 1 2 Four of the ve orbitals are aligned in a different plane The fth is aligned with the z axis dzsquared The third lowest energy orbitals in a principal energy level Mainly fourlobed Planar nodes 2 has ve d orbitals m d Orbitals f Orbitals dzz orbital f xl 7 ZZ orbital fxyz orbital z dzz yz orbital fax 7 ya orbital z z 3 f Orbitals Each principal energy state above n 3 has seven d orbitals m 3 3 The fourth lowest energy orbitals in a principal energy state Mainly eightlobed Planar nodes Phase of an Orbital Orbitals are determined from mathematical wave functions A wave function can have or values The sign of the wave function is called phase When orbitals interact their wave functions may be in phase or out of phase CHAPTER 8 PERIODIC PROPERTIES OF THE ELEMENT Nerve Transmission Movement of ions across cell membranes is the basis for the transmission of nerves signals lon size an other properties of atoms are periodic properties whose values can be predicted base on the element s position on the periodic table Mendekeev Ordered elements by atomic mass Saw a repeating pattern of properties Periodic law Put elements with similar properties in the same column Used patter to predict properties of undiscovered elements Electrons Con gurations Quantummechanical theory describes the behavior of electron in atoms The electrons in atoms exist in orbitals A description of the orbitals occupied by electrons is called an electron conf The properties of the elements are determined by the arrangement of electrons in their atoms This arrangement is understood using the quantum mechanical model developed Electrons have both particlelike and wavelike properties The behavior of electrons can be described using wave function equation Electrons are not perfectly free to move They are restricted to certain energy values or quantized

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