Popular in Organic Chemistry I
Popular in Chemistry
This 7 page Class Notes was uploaded by Faith Han on Thursday September 17, 2015. The Class Notes belongs to CHE 201LLR at University at Buffalo taught by Clizbe, E A in Fall 2015. Since its upload, it has received 31 views. For similar materials see Organic Chemistry I in Chemistry at University at Buffalo.
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Date Created: 09/17/15
Faith Han University at Buffalo CHAPTER 1 Structure Determines Property Atomic Number amp Mass Number Review 0 Mass protons neutrons Atomic protons of protons of electrons Heisenburg Uncertainty Principle Impossible to know the position and velocity of a particle Not important for large objects ie car baseball etc 0 Important for small objects ie electrons Location of electrons look fuzzy Shrodinger Equation 0 Also known as the wave equation Describes electron behavior Gives series of solutions called wave functions LJ Orbitals give the probability of nding an electron at a particular point S Orbitals Has no directionality Energy increases with number of nodal surfaces Nodes are the rings around the nucleus 0 1s no node 2s one node 3s two nodes P Orbitals Dumbbell shape 0 Not present in rst electron shell 0 Three orbitals for each value of n gt 1 Pauli Exclusion Principle two electrons can be in each orbital if they have opposite spins 12 or 12 Principle quantum number the period or row of the periodic table in which an element appears Hund s Rule equal energy orbitals are half lled rst Ionic Bonds Attraction btwn oppositely charged ions ie Na and Cl Na l Na e Na has the same con guration as Neon because Na lost an electron So now they are isoelectronic lsoelectronic same of electrons Covalent Bonds 0 Share electron pairs Nonpolar also known as pure covalent is when electrons are evenly shared ie H2 l H H Formal Charges 1 Calculate of electrons in the element l2bonded pairs lone pairs 2 Find FC valence electrons 12bonded pairs lone pairs 3 Add up each FC to calculate net FC Ex Find the formal charge of HCO3 H 122 O 1 FC 11 FC O C 128 O 4 FC 44 FC O 1226 7 FC 67 FC 1 124 4 6 FC 66 FC O O O O 124 4 6 FC 66 FC 0 NET FORMAL CHARGE 1 Polar Covalent Bonds If an atom has a greater tendency to attract electrons towards itself than the other the electron distribution is polarized also known as electronegativity Ex H F F uorine is more electronegative than H so it pulls electrons towards itself Thus F has partial negative charge and H has partial positive charge Electronegativity increases left to right and decreases top to bottom on a periodic table EX In which of the following is Hydrogen s partial charge the greatest Which one does the Hydrogen bear a partial charge CH4 NH3 H20 D H has greatest partial charge because 0 is the most electronegative SiH4 H25 D H has the greatest partial charge because S is a 2nOI row element and electronegativity decreases top to bottom on the periodic table Dipole Bond dipole moments the product of the amount of the charge quotequot multiplied by the distance between the centers of charge Differences in electronegativity give rise to bond dipoles Greater differences in electronegativity means great bond polarity ie compare the dipole movements of HF and HLi Resona nce Structures Purpose of resonance structures is to connect as many electrons as possible Only electrons move Rule The more resonance structures you can write means the molecule is more stable How to recognize the more stable resonance structure Has as many octets as possible Has as many bonds as possible Has the negative charge on the most electronegative atom Has as little charge separation as possible you want the charges to be as close to each other as possible this only matters if both and charges are included 0 Never start arrows at a charge PWN 0 Ex e IKEI I INEC D H Nl3 3 F I39 II 9 quot9 NCo H Mac D J quot H The last resonancestructure bottom right is the most stable because it has the negative charge on O which is the most electronegative atom VSEPR valence shell electron pair repulsion Most stable arrangement of groups attached to central atom has maximum separation of electron pairs Repulsion from bonded electron pairs is less than nonbonded electron pairs 0 Multiple bonds are considered to be one group of electrons Tetrahedral D 1095 degree angle Molecular Dipole Moment 0 Geometry of a molecule can cause dipoles to cancel ie C02 has a dipole moment O D E l i39 g tvityl 2 EJ r Bronsted Lowry Acid amp Base BL Acid donates protons BL Base accepts protons The reaction a proton is transferred from acid to base 0 EX I quot Hi V baaa aafa aaajagara acid aaajagafa baaa H 1 Bronsted Lowry Acid Strength Keq HO3A HA 0 Strong acid means small pKa value 0 Measures pH pKa log10 Ka if you have the pKa bu not Ka D 10quotpka Determining Relative Acidity of BL Acid 0 Ease of HA bondbreaking Stability of its conjugate base 0 Conjugate base is most unstable charges species in equilibrium 0 Stabilization can be achieved by Electronegativity differences Size differences Resonance stabilization of conjugate base 0 As size increases the H is more loosely held and bond is easier to break 0 Larger size also stabilizes the anion As the bond to H becomes more polarized H becomes more positive and bond is easier to break Electronegative atoms in a molecule can affect acidity even when they are not bonded directly to the ionizable proton EX CH3CH20H ethanol amp CF3CH20H 222tri uroethanol pka 16 pka 113 Ka difference 10quot47 F is very electronegative so they attract electrons and this attraction is transmitted through the bonds increasing the positive character of 0H proton Greater positive character hence increased acidity of the 0H proton of 222tri uroethanol CF3CH20H also has an inductive effect Inductive effect when substituent induces a polarization in the bonds btwn it and some remote site As bonds btwn two units increase inductive effect decrease Electron Delocalization in the conjugate Base Delocalization of the negative charge on the conjugate base will stabilize the anion so the substance is a stronger acid More resonance structures usually means greater stabilization le Nitrate ion AcidBase Equilibria Equilibrium in an acidbase reaction will favor the weaker acid and weaker base Structure effects acidity in 3 ways 0 Bond strength to the atom from which proton is lost 0 Electronegativity of the atom from which the proton is lost 0 Electron delocalization in conjugate base Electronegativity is the most important factor when comparing elements in the same row of the periodic table Equilibrium constant can be calculated from the Ka Keq Ka of reactant acid Ka of product acid 10quotpka of reactant acid 10quotpka of product acid Products favored when Ka gt 1 Reactants favored when Ka lt 1 Stronger acid stronger base weaker acid weaker base K gt 1 gt4 Reaction will be favorable when stronger acid is on the left and weaker acid is on the right Equilibrium also favors dissociation of the stronger acid Knowing approximate pka s allows you to predict the direction of proton transfer The weaker acid high pka is favored Lewis Acids amp Bases Lewis acid electrons acceptor electrophile Lewis base electron donor nucleophile Ex General and speci c example below Fig 2 F L F H H 3 1 1r H N B F F F 1 Eb General 3 139 B A H H N39 Speci c
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