UB CHE 101 - Final Exam Study Guide (7 pages)

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Final Exam Study Guide

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Final Exam Study Guide


This study guide covers part 3 of the course lectures, combined with the other 2 study guides you would have all final exam material.

Study Guide
University at Buffalo, The State University of New York
Che 101 - General Chemistry Lecture
General Chemistry Lecture Documents
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CHE 101 Final Study Guide Chapter 10 Bonding and Lewis Structures Want 8 VE by sharing or having on its own Types of Bonds 1 Metallic share electrons because metals lose electrons easily 2 Ionic transfer electron to get octet a Metals lose and nonmetals gain b Stability more positive more stable 3 Covalent share electron in molecular compounds a More electrons strong bond short bond 4 Possible Bond Distributions Electronegativity Bonded atoms ability to attract electron in bond strength of bond Higher EN means better at attracting electron EN determines amount of sharing o Nonpolar covalent electron shared equally 0 0 4 identical nonmetal atoms o Polar covalent electron shared unequally 0 4 2 different nonmetal atoms o Ionic electron transferred 2 4 Polarity describes electron sharing Dipoles Partial negative charge more electrons around ion Partial positive charge less electrons around ion Atom with higher EN gets partially negative end Lewis Structures Show covalent bonding use VE and octet rule Exceptions to octet rule o Incomplete octet EN too low to get more electrons Be has 2 VE and stable with 4 B has 3 VE and stable with 6 o Expanded Break octet possible for electrons in periods 3 6 Unfilled d orbital or large size of central atom Drawing Lewis Structures 1 Calculate total VE in molecule a V of atoms VE of atoms VE charge 2 Determine central atom least EN atom a H never central atom sometimes can have multiple centrals b C always central and rarely has lone pairs 3 Draw skeleton structure a Single or multiple bonds try for symmetry 4 Fill in octets with lone pair electrons to outer atoms then central a of electrons must equal V from step 1 of bonds 5 Calculate formal charge FC a FC VE unshared electrons of lone e pairs shared 2 b Must add up to charge on molecule c Only indicate non zero charge 2 A 3 A 4 A 5 A 6 A 7 A 2 3 4 3 2 1 0 0 0 1 2 3 Resonance More than one structure can be drawn because of o Presence of multiple bonds and or central atom can break octet with outer atoms capable of multiple bonds Atoms stay but redistribute electrons Use FC to rank resonance o Best structure has lowest FC and or negative FC is on most EN atom Resonance structures blend but don t change back and forth Polyatomic Ions and Acids When turning molecule into acid you add H H attracts to negative part of molecule o Add to structure and determine best place by FC H almost always attaches to O in acids Chapter 9 Molecular Geometry and Bond Theories Geometry creates bond angles electronic geometry is arrangement of electrons around central atom and molecular geometry is arrangement of atoms around central atom Electron Domains of bonding and lone pairs around central atom Resonance structures have same of domains Each central atom has own set of domains Diatomic doesn t equal domain VSEPR 1 Electronic geometry determined by of domains 2 Molecular geometry a Don t consider lone pairs lone pairs and double triple bonds decrease angle between bonding atoms b Molecules with more than 1 central atom means entire molecule is combo of all CAs investigate separately Molecule Polarity Distance of electron in entire molecule Depends on dipoles look at direction and bond strength o Arrows cancel non polar don t cancel polar Molecule Polarity and Resonance Merging resonance structures may change polarity of molecule Individual atoms polarities may cancel and be non polar Valence Bond Theory Covalent bonds form when orbitals of 2 atoms overlap Region is between nuclei and filled with shared electrons pairs mix orbitals 1 Electron in overlap region have opposite sign 2 Greater overlap stronger bond o p d and f orbitals align along long axis 3 Works for diatomic linear molecules Orbital hybridization comes from mixing orbitals o sp sp2 sp3 sp3d sp3d2 o of original atomic orbitals of hybrid orbitals Creating Hybrid Orbitals 1 sp hybrid 2 orbitals make linear electronic geometry and 2 unhybridized p orbitals left over 2 sp2 hybrid 3 orbitals make trigonal planar electronic geometry and 1 unhybridized p orbital left over 3 sp3 hybrid 4 orbitals make tetrahedral electronic geometry and have 0 unhybridized p orbitals left over Shortcut for Predicting Hybridization Draw lewis structure determine domains hybrid superscripts add up to domains Covalent Bonds Depends on how orbitals overlap 1 sigma bond end to end overlap 2 pi bond side to side overlap To form pi bonds atoms can stretch above below molecule Delocalized Bonding Localized electron electron with in plane between Delocalized electron not between only 2 atoms o Sigma electron always localized within plane o Pi electron can localize many ways Compensate for resonance structures by smearing to give extra stability Steric of outer atoms and of lone pair electrons on central atom Chapter 11 Intermolecular Forces and Phase Changes Forces 1 Intramolecular between atoms within molecule a Strong influence chemical properties 2 Intermolecular IMF between atoms of separate molecules a Weak influence physical properties melting boiling pt b Vander Waal s forces Types of IMF Forces 1 London Dispersion electron movement causes instantaneous dipole temporary partial charge o Present in all compounds ionic polar and non polar o IMF increase with increase in molecular weight and more linear shape 2 Dipole Dipole attraction between neutral polar molecules o Positive end near negative end stronger than London o IMF increases with more polar molecules o High boiling point high IMF 3 Hydrogen bonding extra strong dipole dipole o H bonded with N O F 4 Ion dipole between ions and partial charge of polar molecule o Occur when ionic compounds dissolve in water o Increase IMF with charge of ion and magnitude of dipole Can have more than 1 force in a molecule States of Matter PE how molecules are held together o Charge and distance IMF KE distance of molecules in container o Speed and temperature Liquid 1 Viscosity resistance of liquid to flow a IMF strong long molecular chain high viscosity b High temp decreases viscosity fast molecules overcome IMF 2 Surface tension energy required to stretch or increase surface a Molecule imbalance of IMF i Interior attracted equally and surface attracted inward b Strong IMF high surface tension 3 Capillary Action rise of liquid through narrow tube against gravity a Cohesive IMF between liquid molecules b Adhesive IMF between liquid and tube walls Changing Phase By forcing or breaking IMF High temp endothermic break IMF low temp exothermic

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