Preview Homework due before every class period by 9 AM First LearnSmarts are due a week from today Purchase McGraw Hill Connect Code to access homework Chapter Homework due one week after the chapter is nished 1 1 Atoms Electrons Orbitals gen chem review Atomic Number 2 number of protons Electrons e negative portion of the atom Electrons are the ones that do chemistry Orbitals where the electrons are located within the atom Quantum Numbers helps locate electrons within the atom Principle n how far energy level angular momentum l shape of the orbital magnetic quantum m2 3D orientation spin ms positive or negative spin Pauli Exclusion Principle no two electrons will have the same four quantum numbers in an atom individual locations Shapes of orbitals Valence Electrons outer electrons Isoelectronic same number of electrons Octet Rule Noble gas con guration WANT 8 Builds compounds One type of bond IONIC vs COVALENT Charged Share Steal electrons Cations Na Ionization Energy Anions e Cl g Cl g Electron Af nity Ionic bonds formed Na Cl NaCl How is it so stable strength of charge used mostly in inorganic compounds so what is plan B 1 3 Covalent Bonding shared model LEWIS STRUCTURES 2D model of a molecule Shared electrons dashed line Unshared electrons dots one atom Examples draw methane CH4 ethyl bromide C2H5Br 8e What happens if the octet rule isn t achieved Double Triple Bonds 1 4 Double Triple Bonds Prime Examples Ethylene C2H4 Double bond 4e shared between 2 atoms Triple bond 6e Examples Formaldehyde CH2O Hydrogen cyanide HCN 1 5 Polar Bonding Are electrons shared equally NO Electronegativity Representation of bond polarity DELTA NOTATION vs ARROW NOTATION One other way electrostatic potential map Rainbow colors to show charge distribution BLUE show positively charged ends while RED show negatively charged sides Trends of electronegativity polarity Periodic table Dipole moments X Y 1 Strength 2 Bond length Indicate the direction of dipole moment Size and direction of dipole can hint at reaction types When species have charges NH4 is the charge on one atom Formal Charge Book Formula Group number electron count FC 1 2 shared unshared Electron count 8e N 4 H 1 Dr C easy formula FC what you start what you get 5 4 1 Electrons move delocalization Reason for formal charge Electron bookkeeping Don t lose electrons 1 7 Structural Formulas more complex the larger they get more connections and more variety need a system Example C2H7N many variations 1 Determine molecular formula Charges of individual atoms MUST equal overall charge of the compound if compound is 1 1 etc atoms must add to that Realization of formal charge 2 Count valence electrons 20e 3 Connect all bonded atoms using dashes for a shared electron 4 Count all used electrons and subtract from total count 5a Add electrons until atoms have 8e around them octet rule or run out 5b If one or more atoms has fewer than 8e use unshared electrons pari to form double or triple bonds 6 Calculate formal charges more stable better What if the same molecular formula give different structure Isomers Two types constitutional structural different connectivity stereoisomers CH 7 When does formal charge determine structures Example methyl nitrate CH3NO2 Number of electrons 24 Rules for formal charges 1 8 Resonance 1 Smaller charges are better O is most stable for most organics 2 Adjacent atoms prefer opposite charges while destabilized by similar charges 3 Negative formal charges preferred location electronegative atoms What happens if we can draw more than one structure for a molecule Example carbonate ion CO32 Proof that all three structures contribute to the experimental results All bonds are same length Resonance two or more Lewis structures the differ by Resonance hybrid true structure of the various structures Resonance s role on electrons localized shared between two atoms or unshared lone pair delocalized free owing electrons easiest way to show delocalization curve arrow system Are all resonance structures equivalent GENERAL RULES OF RESONANCE 1 Connectivity must be the same no atom movement only electrons 2 Structures must have the same number of electrons and the same net charge formal charge on atoms may vary 3 Must have same number of unpaired electrons no radicals made 4 Don t break Octet rule 10 e is not allowed Resonance Contributions 1 The greater number of shared covalent bonds contributes more to stability Don t violate Octet rule 2 Little separation of charged No same charges 3 Negative formal charges on electronegative atoms O Cl F N 1 9 Writing Organic Structures Chemists are lazy Many differ representations that highlights different things CH3CH2OCH2CH3 condensed formula Condensed formulas leave out many of the covalent bonds lone pairs and use subscripts for identical groups attached to atoms Examples CH3CHCl2 Condensed is good but we can get lazier and draw structures faster Bond line formula skeleton structures CH3CH2CH2CH3 1 Carbon at every vertx unless noted otherwise or at the end of the line 2 Hydrogens are typically omitted 3 When atom is neither C or H it is shown with necessary H atoms heteroatom Examples Expand this structure show all atoms 1 10 Shapes of Molecules Review of molecular geometry for gen chem CH4 methane H2O water Valence shell electron pair repulsion model VESPR model Unshared electrons dominate Electrons want to get away from each other Multiple bonds double and triple are treated as one unit Useful prediction for geometry but not perfect Combination of molecular geometry and bond polarity 1 11 Molecular Dipole Moments Is carbon dioxide polar What about chloromethane CH3Cl Both bonds are polar But molecular is not polar 1 12 Chemical Reactions and Curved Arrows Predicting chemical reactions depends on movement of electrons Two types of curved arrows 2 electrons 1 electron Reactions that you were used to in gen chem looked like AB A B are thought of as A B A B Acid dissociations loss of H Combination reactions A B A B Rule of thumb Electrons ow from high density to low density Example Multiple Arrows Arrow pushing bonds forming and breaking This is very useful for reactions with double triple bonds one component pair is used