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# PRINCIPLES OF CHEMISTRY I CH 301

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This 3 page Class Notes was uploaded by Brady Spinka on Monday September 7, 2015. The Class Notes belongs to CH 301 at University of Texas at Austin taught by Staff in Fall. Since its upload, it has received 42 views. For similar materials see /class/181885/ch-301-university-of-texas-at-austin in Chemistry at University of Texas at Austin.

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Date Created: 09/07/15

McCord CHAPTER 5 Fall 2005 Exam 3 Review Topics Chapter 5 Which Sections for the Exam Chapter 5 Definitely all of sections 18 Then you need to know his of sections 9 through 16 7 YOU get to decide how much YOU want to know on those sections Carry over from previous chapters In order to understand the discussion about dipoles and partial charges you MUST know what those are and what polarity is Chapter 3 introduced this concept You should also still know your periodic table trends 7 especially size and electronegativity Why molecules stick lfmolecules had no sticking power all substances would be gases There would be no condensed phases of solid or liquid Well thank goodness there ARE forces of attraction the sticky between molecules These forces are called intermolecular forces These are the forces that we are most concerned with in chapter 5 These are also the forces that govern various physical properties such as boiling point melting point heat of fusion heat o vaporization surface tension viscosity etc I ll come back to this afterl remind you of the forces of attraction that we have all ready covered quite extensively Intramolecular forces are the forces of attraction within molecules and are simply the bonds that hold the atoms together to make the molecule in the first place Realize that intermolecular forces are much much less than intramolecular forces At least 10 times less and possibly 1000 times less depending on what you are comparing Looking back to chapter 2 you can see how strong an intramolecular force covalent bonding really is Check out Table 23 on page 75 to see numerous bon dissociation energies Those are the amounts of energy that would be required to pull those bonds apart The lowest value on that table is 157 kJmol and goes up to 837 kJmol Realize that is just a sampling of all the possible covalent bond strengths but you need to have an idea of where all those strength are on the energ scale 7 I d ballpark figure these at around 400 kJmol Now let s get back to the main topic here Intermolecular forces All intermolecular forces are governed by charges attracting or repulsing one another Heck pretty much everything chemically speaking can be traced back to this fundamental interaction of charges Bearing that in mind it is still not just a simple case of positive attracts negative We want to quantify the amount of attractionrepulsion so that we can better understand and predict the properties that are a result of these intermolecular interactions IonIon interaction 1 really hate putting this down as a true intermolecular force It is certainly a great force 7 just as strong and as powerful as the intramolecular forces of covalent bonds lonion interaction 18 the reason we have ionic compounds All ionic compounds are solids because of this great big pull that cations have on anions and vice versa lonion interaction is what gives us the large values for the crystal lattice energy of salm ie ionic compounds The potential energy Ep of this interaction is EP 0C Z1Z2 r Where 21 and z are the charges on the two ions and r is the distance between them It s worth noting that when oppositely charged ions are involved positivenegative the potential energy is lowered negative values Positive higher potential resulm when like charges come together Iondipole interaction You got half of the strong interaction of ionion but you ve lost the other half to a mere dipole Dipoles truly deserve the word partial in partial charge Only a little bit of charge is there a little positive 6 and a little negative 639 Although there is variability in the amounm of these charges think electronegativity scale they are still piddly little compared to full charge like cations and anions The potential energy will be less negative now le E on 7 P r2 Where u is the dipole strength These forces are not influential until the distance is considerably small 7 note the lr2 dependence Dipoledipole interaction We now knock down the strength of the interaction even more Dipoledipole interaction is 5ng r Where a is the dipole strength Now the distance dependence is lr3 And this is only if the molecules are relatively stationary like in a liquid or solid In a gas the dipoledipole interaction is reduced further due to fast rotation of the molecule This effectively blurs the partial charges to even smaller values and the resulting potential energy interaction is 2 2 MM Epm r McCord Exam 1 Review Sheet Spring 2006 Which ChapterSections are covered All of Chapter 1 7 that s it All material covered on homeworks l3 Concentrate on the subject matter I emphasized in class and on the homeworks Come in mentally prepared to answer at least 20 questions maybe more Yes there will be calculations but most of the exam will be theory and concepts You need to understand the theory and concepts 7 getting a homework question right does not necessarily mean you really understand the material Energy traveling at the speed of light Know what electromagnetic radiation is and how we depict it on the page and conceptually Know the basics of the entire electromagnetic spectrum see Figure 13 p 3 Know the approximate wavelengths for each type of radiation given LOOK at that figure Know also that visible light is in the 400 700 nm range that s blue end to red end Other than the two ends I do not expect you to know the wavelengths of all the colors of the rainbow 7 however you SHOULD know the ordering of the colors think Roy G Biv Know the two basic equations that describe electromagnetic radiation Ehv cW Know how to use this equations to calculate various wavelengths frequencies and energies of photons Know the two views of electromagnetic radiation as a wave and as a particle photons All moving particles have wavelength Yes Louis de Broglie said if light can be treated as a particle photon then why not the other way around Any moving particle with mass andvelocity should have a corresponding wavelength h h A i 7 where p is momentum p mv p mv The most important moving object for us is the electron Now we can treat the electron as a wave When confined to the region around the nucleus the electron behaves as a Standing wave What is the essence observations of the photoelectric effect p 6 How did Einstein explain this effect How does this relate to the work function 1 of a metal mv2 11V I Be able to calculate any part of this equation m v I or y ifgiven any 3 of the 4 variables in it That thing is REDhot What are the characteristics of blackbody radiation See Figure 14 p 4 for a good idea Note the range of wavelengths for a blackbody radiator They depend on the temperature How does the spectrum shift with temperature Where is the maximum intensity of radiation Use Wein s law for that one TAmax cz where c is the second radiation constant Realize the stark contrast in spectra between blackbody radiation and The Emission Spectrum of Hydrogen Check out those lines Lines 1 tell you Not broad bands of continuous wavelengths but very very narrow precise lines It s like hydrogen is speaking to us What is it saying It is saying I have quantized energy levels When I m excited I spit out very specific quanta of energy Who listened Several smart guys but lem chalk one up for Bohr for realizing that the photon that is emitted is due to the energy difference in quantum levels within the atom As an electron falls from an excited state to a lower energy state a photon is emitted that corresponds to the energy gap Other s put some real math on the energies Balmer but Rydberg came up with a very insightful equation 1 1 V 917 i2 n1 l 2 n2 n1l n12 quot1 quot2 You can use this equation to calculate all kinds of energy transitions You need to know the fundamental difference in the Balmer series and the Lyman series p 18 But WHERE exactly IS the electron What is the Heisenberg uncertainty principle Yes the equation is Apr 2 7L but what does this really mean Can we precisely know the momentum AND position of the electron in the atom Schrodinger s Equation h2 d2 7i Vow Ezp 2m dx Impressive isn t it Can you say differential equation I knew you could What s it for What comes out of it Can it be solved exactly for all atoms Particle in a box Standing Waves Yes if we confine a particle in avery very small space is wavelike behavior starts taking over Only certain waves will fit into the box Tadal These waves are quantized Each wave has a specific wavelength and energy associated with it Once solved let s look at the formula for the energy levels rith 8mL2 What is so significant about this equation Why did we even bother to talk about it What can be learned from this How is this a nice friendly segue into the various solutions to the Schrodinger equation Compare and contrast the similarities of this equation and the equation that Schrodinger arrived at for the energy levels within the hydrogen atom quot n2 811383 n123 n123 How would these two solutions look graphically See Figure 117 p 14 and Figure 122 p 18 Quantum Numbers Know the names symbols and values for the four quantum numbers n 1 ml and ms Principal Quantum Number n 1 2 Angular Momentum Quantum Number 1012n1 Magnetic Quantum Number mll101l Spin Quantum Number ms 12 12 Out from these quantum numbers and the solution to the Schrodinger equation comes wav efunctions What does the wavefunction 1p tell us Ultimately it allows us to map out in three dimensions the likelihood of finding an electron in a given amount of space This is what gives us the orbitals of the hydrogen atom that we are now all familiar with Know your orbitals Know the basic differences in each orbital type S p d andf Your should even be able to follow the trend to g h 139 etc What do nodes have to do with the shapes of these orbitals What kind of nodes are there in these orbitals Answer There are nodal planes nodal cones and nodal spheres aka radial nodes How do these influence the shapes of atomic orbitals More questions to get straight What s the maximum number of electrons that will fit into ANY orbital Each orbital type S p d comes in sew How many orbitals per set What is the maximum number of electrons per set What are the relative energies of the various orbitals for the hydrogen atom for other atoms Electron Configurations You should be able to write OK pick out the answer from a list out the electron configuration of any element on the periodic table Yes you WILL have your own copy of the periodic table to use You should also be able to write out electron configurations for various ions whether cations or anions Know which ions are isoelectronic with one another The Periodic Table First off this thing will really help you out with those electron configurations Second you can really learn a lot about elemenm by studying the trends in the table What do you know You know what and where are the alkali metals Same goes for the alkaline earth metals the halogens and the noble gases Where are the metals nonrnetals and metalloids What are the d transition metals ftransition metals Know what the following are definitions AND what their trends are on the periodic table Atomic Radii Ionic radii ionization energies electron affinities What Equations do you have to memorize You should memorize all the equations on this review sheet with the green background green background Other equations will be given if necessary ALL constants that go into the equations will be given Standand Disclaimer Any mistakes on this review sheet are NOT intentional You should crosscheck all stated information You should double check your book too see errata

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