Chapter 9, 10, & 11

Chapter 9, 10, & 11 - General Chemistry I Fall 2007...

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Unformatted text preview: General Chemistry I Fall 2007 Joann S. Monko Chemistry 9th ed. Raymond Chang Using Bond Energies 2 H--H + Cl--Cl ----> 2 H--Cl Net energy = Hrxn = = energy required to break bonds -- energy evolved when bonds are made Hrxn = D (bonds broken) - D (bonds formed) H--H = 436 kJ/mol Cl--Cl = 242 kJ/mol H--Cl = 432 kJ/mol Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 3 Using Bond Energies 2 H--O--O--H O=O + 2 H--O--H Is the reaction exo- or endothermic? Which is larger: A) energy req'd to break bonds B) or energy evolved on making bonds? H-O = 463 kJ/mol O-O = 146 kJ/mol O=O = 498 kJ/mol 2144 kJ/mol 2350 kJ/mol Hrxn = -206 kJ/mol exothermic Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Bond Polarity + - 4 HCl is POLAR -it has a positive end & a negative end. H Cl Cl has a greater share in bonding e-'s than does H. Cl - slight negative charge (- ) H - slight positive charge (+ ) H is + (red) and Cl is - (yellow) Calc'd charge is + or - 0.20 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Electronegativity, - a measure of the ability of an atom in a molecule to attract electrons to itself. 5 TWO unshared Nobel prizes: Peace & Chemistry Chemistry areas: bonding, electronegativity, protein structure Concept proposed by Linus Pauling 1901-1994 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. + - H Cl Bond Polarity 6 The H--Cl bond energy is GREATER than expected for a "pure" covalent bond. ENERGY 339 kJ/mol calc'd 432 kJ/mol measured BOND "pure" bond real bond Difference = 92 kJ. proportional to the difference in ELEC TRONEGATI VI TY, . Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Electronegativity 7 Chemistry 8th ed. Raymond Chang 8 4 3.5 3 O N C H F Cl S Si P Electronegativity 2.5 2 1.5 1 0.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 F = maximum . Lowest Atom = center atom Relative values of BOND POLARITY (& point of attack on a molecule) Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Bond Polarity Which bond is more polar (or DIPOLAR)? O--H 3.5 - 2.1 1.4 0.5 O--F 3.5 - 4.0 9 OH is more polar than OF - O + H + O - F polarity is "reversed." Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Molecular Polarity Boiling point = 100 C 0 10 Boiling point = -161 C Why do water and methane differ so much in their boiling points? Why do ionic compounds dissolve in water? Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Why do CuCl2, acetic acid, and ethanol dissolve in water? 0 11 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Molecular Polarity Molecules (HCl and H2O) can be POLAR. 0 12 They have a DIPOLE MOMENT. The polar HCl molecule will turn to align with an electric field. Figure 9.15 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Dipole Moments, 0 13 The magnitude of the dipole is given in Debye units. Peter Debye (1884 - 1966). Rec'd 1936 Nobel prize: x-ray diffraction & dipole moments. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Molecular Polarity Molecules will be polar if a) bonds are polar AND b) the molecule is NOT "symmetric" 0 14 All above are NOT polar! Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Polar or Nonpolar? 2 2 0 15 Compare CO and H O. Which one is polar? CO is NOT polar even 2 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. -0.75 +1.5 -0.75 though the CO bonds are polar. CO is symmetrical. 0 16 Polar or Nonpolar? Consider AB molecules: BF , Cl CO, and NH . 3 3 2 3 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 17 Clicker Question Consider the molecule SO2 1. Polar bonds, polar molecule, 1.5, S = +1 2. Polar bonds, nonpolar molecule, 1.5, S = -1 3. Polar bonds, nonpolar molecule, 1.5, S = +1 4. Nonpol. bonds, nonpol. molecule, 1.5, S = -1 5. Polar bonds, nonpolar molecule, 2, S = +1 6. Polar bonds, polar molecule, 2, S = -1 7. Polar bonds, polar molecule, 2, S =+1 Mole cular Polarity, BF & HBF F B F F 3 0 18 B is + atoms are - 2 F B--F bonds are polar molecule is symmetrical NOT polar B is + & F atoms are but H H B F F B--F & B--H bonds are polar. The molecule is NOT symmetrical & IS polar. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 19 Is Methane, CH , Polar? 0 4 Methane is symmetrical & is NOT polar. I s CH F Polar? 3 C--F bond is very polar. Molecule is not symmetrical & is polar. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Substituted Ethylene 0 20 C--F bonds are MUCH more polar than C --H bonds. Because both C--F bonds are on same side of molecule, molecule is POLAR. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Substituted Ethylene 0 21 C--F bonds are MUCH more polar than C--H bonds. Because both C--F bonds are on opposing ends of molecule, molecule is NOT POLAR. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 0 22 Consequences of H2O Polarity Microwave oven Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Chemistry, 8th ed. Chang Inter-molecular Forces 23 0 B4 studied INTRAmolecular forces -- the forces holding atoms together to form molecules. Now look at between molecules -- INTERmolecular forces. Forces between molecules, between ions, or between molecules and ions. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 24 0 Ion-Ion Forces for comparison of magnitude Na+--Cl- in salt These are the strongest forces. Lead to solids with high melting temperatures. NaCl, mp = 800 oC MgO, mp = 2800 oC Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 25 0 Attraction Between Ions & Permanent Dipoles water - dipole O H H + Water is highly polar & can interact with positive ions to give hydrated ions. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Attraction Between Ions & Permanent Dipoles Many metal ions are hydrated. This is the reason metal salts dissolve in water. 26 0 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Attraction Between Ions & Permanent Dipoles Mg2+ - H O H + 27 0 Na + - H O H + - H O H + -1922 kJ/mol -405 kJ/mol Cs+ -263 kJ/mol Attraction between ions and dipole depends on ion charge and ion-dipole distance. Measured by H for Mn+ + H2O --> [M(H2O)x]n+ Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 28 0 Dipole-Dipole Forces Such forces bind molecules having permanent dipoles to one another. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 29 0 Dipole-Dipole Forces Influence of dipole-dipole forces is seen in the boiling points of simple molecules. Compd Mol. Wt. Boil Point N 28 -196 C Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Hydrogen Bonding 30 0 A special form of dipole-dipole attraction, which enhances dipole-dipole attractions. H-bonding is strongest when X and Y are N, O, or F Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Hydroge Bonding be e n twe n... Me thanol (C OH) & H O H 31 0 Two m thanol m cule e ole s 3 2 - + - + - - Hydrogen bond Hydrogen bond Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 32 Clicker Question Arrange the following in order of increasing boiling points: RbF, CO2, CH3OH, CH3Br 1. RbF < CO2 < CH3OH < CH3Br 2. CH3OH < CO2 < CH3Br < RbF 3. CO2 < CH3Br < CH3OH < RbF 4. CH3Br < CH3OH < RbF < CO2 5. CH3Br < RbF < CO2 < CH3OH Hydroge Bonding be e Am onia n twe n m (NH ) & H O 3 2 33 0 - + - H-bond This H-bond leads to the formation of NH4+ and OHKotz &Treichel Chemistry & Chemical Reactivity 5th ed. Hydroge Bonding in H O n 2 34 0 H-bonding is especially strong in water because... the O--H bond is very polar there are 2 lone pairs on the O atom Accounts for many of water's unique properties. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Hydroge Bonding in H O n 35 0 2 Ice has open lattice-like structure. Ice density is < liquid. And so solid floats on water. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 36 Boiling Points of Simple Hydrocarbon Compounds H bonds leads to abnormally high boiling point of water. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. ...
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This note was uploaded on 04/08/2008 for the course CHEM 100 taught by Professor Monko during the Winter '08 term at Kutztown.

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