Chapter 11 part 1 Intermolecular forces Read HW INTERMOLECULAR IM FORCES Noncovalent interactions chemical bonds intramolecular forces 150 1100 kJ mol BLB 11 1 2 11 6 BLB 11 9 15 21 23 25 27 Supplemental 11 1 4 Know intermolecular forces 1 electrostatic interactions 2 dispersion forces 3 dipole dipole interactions 4 hydrogen bonds H bonds What Bonus Deadlines are coming up When is Exam 2 Where do I go for Exam 2 intermolecular IM forces 1 50 kJ mol intermolecular interactions forces that hold covalent molecules together in groups Which homework reading am I finished with Molecular Composition Organic Geometry VSEPR Polarity Hybrid orbitals Bond Types Resonance Intermolecular Forces general classes of IM interactions 1 electrostatic interactions 2 dispersion forces 3 dipole dipole interactions 4 hydrogen bonds H bonds Dr Lori S Van Der Sluys Dr Lori S Van Der Sluys Page 1 Chapter 11 Page 2 Chapter 11 Why doesn t everything exist as a gas Kinetic Molecular Description of Liquids and Solids IMF Non covalent Interactions chemical bonds intermolecular IM forces 150 1100 kJ mol 1 50 kJ mol Relative strengths of intermolecular forces can be seen experimentally gas Kinetic energy intermolecular forces liquid Kinetic energy intermolecular forces solid Kinetic energy intermolecular forces What kind of attraction What happens as intermolecular distances decrease Strength of IM forces depends on Q Kinetic Energy T Cooling T KE gas liquid solid charge on ion dipole moment polarizability Define Polarizability increases as increases as Dr Lori S Van Der Sluys Page 3 Chapter 11 Dr Lori S Van Der Sluys Page 4 Chapter 11 ELECTROSTATIC FORCES TYPES OF INTERMOLECULAR FORCES Depends on Ion Ion ionic bond Q Ion Dipole Ions in aqueous solutions of electrolytes Q Dipole Dipole Ion Induced Dipole ions in nonpolar solvents Q Dipole Induced Dipole polar molecules in nonpolar solvents Dr Lori S Van Der Sluys Page 5 E Q1Q2 d Ion Dipole Q E Q d2 2 E 1 2 d3 Dipole Dipole Dispersion induced dipole induced dipole Hydrogen Bonding must have H bonded DIRECTLY to N O or F Ion Ion 1 directional dipole dipole Chapter 11 Dr Lori S Van Der Sluys Page 6 Chapter 11 LONDON DISPERSION FORCES LDF E 1 62 d ALL molecules have LDF Interactions Ar Ar Induced Dipoles Na Ar H Cl Cl H in addition to dipole dipole Dispersion forces are related to 1 2 Size is related to London Dispersion forces Induced dipoles induced dipoles forces Ease of electronic distortion is What s happening to the electrons Is there a dipole moment What happens to neighboring molecules Dr Lori S Van Der Sluys Page 7 Chapter 11 Dr Lori S Van Der Sluys Page 8 Chapter 11 HYDROCARBONS ALKANES H H C H H H H C H C H H H H H H H C C C H H H C C C C C straight chain ALKENES H H C H H C C C H H H CH 3 ALKYNES H C C H CH3 C C H AROMATIC HYDROCARBONS H H H C C C C H C C H SHAPE Affects the amount that two molecules can interact the more interaction the more LDF 5 Carbon Alkanes n pentane BP 36 2 C H H H H C C H C C C C H neopentane BP 9 5 C C C C C C branched H H 2 methyl butane is in between Are Alkanes polar BP 28 C What kind of IMF Dr Lori S Van Der Sluys Page 9 Chapter 11 Dr Lori S Van Der Sluys C C C C C Page 10 Chapter 11 Effect of Hydrogen Bonding on BP of water Hydrogen Bonding H bonded directly to a very electronegative atom N O F interacts with lone electron pairs on N O F of another molecule H bond energies are 4 25kJ mole H O H Strong IMF s Weak compared to H covalent bonds but are directional like covalent bonds H O Hydrogen Bonding Explains why ice floats on water double helix in DNA helix in proteins The effect of hydrogen bonding is also seen in the abnormally high boiling points of NH3 and HF Dr Lori S Van Der Sluys Page 11 Chapter 11 Dr Lori S Van Der Sluys Page 12 Chapter 11 Importance of H bonding in DNA RNA Helix structure for a protein is held together by hydrogen bonding interactions Polymers high molecular wt materials formed from many small molecules called repeating unit nucleotides 4 organic bases bind specifically in pairs DNA double helix is held together by hydrogen bonding interactions Dr Lori S Van Der Sluys Page 13 Chapter 11 Dr Lori S Van Der Sluys Page 14 Chapter 11 How do you know which has the strongest IM forces compare B P and M P higher B P M P means stronger IM forces If substances are similar follow trends Example inert gases Is shape different What happens to BP as MW increases Energies of Interaction Types Type Covalent Example kJ mol C C Electrostatic 450 33 ion ion Na Cl If trends compete need BP or MP ion dipole Na CF3H Eg dipole dipole CF3H CF3H CH3Cl CH3Br CH3I 24 2 C 3 6 C 42 4 C increases size polarizability increases 350 2 London dispersion CF4 CF4 2 Hydrogen Bonding H2O H2O 24 London Dispersion forces dominate here Dr Lori S Van Der Sluys Page 15 Chapter 11 Dr Lori S Van Der Sluys Page 16 Chapter 11 IMF Effect on BP Type Example BP C C graphite 4827 Ion ion NaCl 1413 H bonding H2O 100 DipoleDipole CHF3 82 London Dispersion CF4 129 Covalent Figure 11 12 Flowchart for determining intermolecular forces What happens to all intermolecular interactions at the boiling point What happens to the BP if the interaction is strongest Dr Lori S Van Der Sluys Page 17 Chapter 11 Dr Lori S Van Der Sluys Page 18 Chapter 11 Which intermolecular forces are important in the hydrocarbon 1 2 3 4 5 LDF only LDF and dipole dipole LDF dipole dipole H bonding only dipole dipole only H bonding Which intermolecular forces are important in the carboxylic acid 1 2 3 4 5 LDF only LDF and dipole dipole LDF dipole dipole H bonding only dipole dipole only H bonding Which intermolecular forces are important in the aldehyde 1 2 3 4 5 LDF only LDF and dipole dipole LDF dipole dipole H bonding only dipole dipole only H bonding Dr Lori S Van Der Sluys Page 19 Chapter 11
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