Lecture 20 Intermolecular forces 2 Read HW BLB 11 1 2 11 6 BLB 11 9 15 21 23 25 27 Sup 11 1 4 Know intermolecular forces ion dipole dipole dipole London dispersion forces hydrogen bonds phase diagrams Exam 2 Monday March 2 6 30 review previous material so you UNDERSTAND what we ve done and what we are doing now and start preparing now Final Exam Monday May 4 12 20 MUST register on elion for a final exam conflict or overload by March 8 See http www registrar psu edu exams exam overload cfm http www psu edu dus handbook exam html conflict Need help Get help TAs in CRC 211 Whitmore and Supplemental Instruction SI hours on Chem 110 website Sheets office hours Mon 12 30 2 Tue 10 30 12 in 324 or 326 Chem Bldg Sheets Page 1 Lecture 20 Hydrogen bonding hydrogen bonding H bonding H covalently bonded to a very electronegative atom N O F interacts with lone pairs of e on N O F of another molecule dipole dipole IMF directional similar to covalent bonds H bond energies 4 25 kJ mole which is strong as intermolecular forces go but much weaker as compared to covalent bonds http wps prenhall com wps media objects 602 616516 Media Assets Chapter10 Text Images FG10 06 02UN JPG Sheets Page 2 Lecture 20 Hydrogen bonding cont H bonding why ice floats on water double helix in DNA helix in proteins Sheets Page 3 Lecture 20 Water water everywhere H bonding IM force BUT directional ala a covalent bond it s a directional dipole dipole IMF manifestations of strong IM forces in water high surface tension capillary action in plants high specific heat moderate temperatures near oceans lakes high heat of vaporization regulation of body temperature sweat condensation in clouds fuels thunder storms because H bonding occurs ice floating on water ice has lower density than liquid water note backward slope on phase diagram ice on surface of lakes oceans insulates rest of water keeps entire lake oceans from freezing ice melts as pressure increases ice skating Sheets Page 4 Lecture 20 H bonding in your body H bonding allows you and every other lifeform to exist really DNA RNA proteins are biological polymers polymers are high molecular weight materials formed from many small molecules which are called monomers repeating unit monomers nucleotides amino acids Sheets Page 5 polymers RNA DNA proteins Lecture 20 H bonding in DNA nucleotides 4 bases H bond in specific pairs adenine thymine guanine cytosine BLB Figs 25 40 25 41 25 42 H bonds stabilize double helix structure play critical role in replication H bonding in proteins protein folding e g helix BLB Fig 25 26 protein protein interactions recognition e g signaling Sheets Page 6 Lecture 20 Sheets Page 7 Lecture 20 How do you know which molecule has the strongest IM forces compare boiling points melting points BP MP means stronger IM forces if substances are similar follow trends example inert gases have similar shapes IM forces as MW Lecture 19 p 14 competing trends need BP or MP CH3Cl 1 87 D CH3Br 1 81 D CH3I 1 62 D size MP 24 2 C 3 6 C 42 4 C LDF dominate in this particular example Sheets Page 8 Lecture 20 Let s compare strength of IM forces for different functional groups IM functional MW forces BP structure group g mol at work hydrocarbon 36 C CH3CH2CH2CH2 CH3 72 O aldehyde 75 C CH3CH2CH2 C 72 H O ketone ether 79 C CH3CH2 C 34 C CH3CH2 O 72 CH3 CH2CH3 74 O ester alcohol 57 C CH3 C 74 OCH3 117 C CH3CH2CH2CH2 OH 74 O carboxylic 141 C acid Sheets CH3CH2 Page 9 C 74 OH Lecture 20 Before next class Review Lectures 13 20 Chap 3 9 organic chem Please bring any last minute questions you may have This is for touch up or clarification questions NOT a lecture repeat Bring printouts Sheets Page 10 Lecture 20
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