CHM 112 M. Prushan Chapter 10 Liquids, Solids, and Phase Change.

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CHM 112 M. Prushan Chapter 10 Liquids, Solids, and Phase Change

CHM 112 M. Prushan Why Do Solids and Liquids Exist? Intermolecular Forces gases – Little to no attraction between molecules

CHM 112 M. Prushan Why Do Solids and Liquids Exist? Intermolecular Forces liquids – Fairly strong forces between a few molecules

CHM 112 M. Prushan Why Do Solids and Liquids Exist? Intermolecular Forces solids – Strong forces prevent large amount of motion between molecules/atoms

CHM 112 M. Prushan What makes a molecule polar? Polar molecules are said to possess a permanent dipole moment. Dipole moment measured in units of Debye (Q x r ) [charge x distance] 1 D = 3.336 x 10 -30 coulomb meters Prof. Peter Debye Noble Prize 1936

CHM 112 M. Prushan Dr. Prushan, enough physics, what does it mean? OK… Let’s go back to Lewis Structures and VSEPR Examples: Draw Lewis Structures and Predict the Geometry of : NH 3, H 2 O, CH 4, CH 3 Cl,CHCl 3 CO 2, CCl 4 (Yes, there was a reason you needed this)

CHM 112 M. Prushan Examples NH 3 H2OH2OCO 2 Trigonal PyramidalBentLinear Tetrahedral CCl 4 CH 3 ClCH 4 CHCl 3

CHM 112 M. Prushan Polar or Not Polar That is the Question? NH 3 H2OH2OCO 2 Trigonal PyramidalBentLinear

CHM 112 M. Prushan Polar or Not Polar That is the Question?  = 1.47 D  = 1.85 D  = 0 D  +  -  +  -  + NH 3 H2OH2OCO 2 Trigonal PyramidalBentLinear

CHM 112 M. Prushan Polar or Not Polar That is the Question? CCl 4 CH 3 ClCH 4 CHCl 3  +  -  +  = 0 D  = 1.87 D  = 1.90 D

CHM 112 M. Prushan Types of Intermolecular Forces 4 main types of intermolecular forces (1) London (Dispersion) Forces (2) Dipole-Dipole Forces (3) Ion-Dipole Forces (4) Hydrogen Bonds Increasing Strength

CHM 112 M. Prushan London (Dispersion) Forces Weakest of the IM forces. All molecules have Dispersion forces Result of interactions between instantaneous dipole moments. Prof. Fritz London

CHM 112 M. Prushan Dipole-Dipole Forces Result of permanent dipole moments in polar molecules

CHM 112 M. Prushan Ion-Dipole Forces The force which dissolves ionic compounds A result of interactions between ions and solvent molecules

CHM 112 M. Prushan Hydrogen Bonds Strongest of the intermolecular forces NOT a chemical bond MUST contain hydrogen covalently bonded to F, Cl, O or N. Essential for Life!

CHM 112 M. Prushan If the boiling point of CO 2 is, and CS 2 is Molecules with larger molecular weights have higher boiling points. So why is H 2 O a liquid, but H 2 S is a gas? Hydrogen Bonds

CHM 112 M. Prushan BONDS… Hydrogen Bonds

CHM 112 M. Prushan Why are Snow Flakes Hexagons?

CHM 112 M. Prushan Hydrogen Bonds and Life Life Depends of H-bonds The “Stuff” of Life relies on them to stay together Proteins, EnzymesNucleic Acids (DNA, RNA) Amino Acids Sugar-phosphate Backbond and Base Pairs

CHM 112 M. Prushan Amino acids bond together to make polypeptides The polypeptides fold to make the secondary structure of proteins How and Why does the alpha structure form?? Linus Pauling Discovered How, in 1948 While in bed with a cold…. Lets let him describe how…

CHM 112 M. Prushan Now let’s try that… Come on down and get a polypeptide

CHM 112 M. Prushan

Hydrogen Bonds are also important in DNA

CHM 112 M. Prushan Which goes with which ??? A – T G – C Right??? BUT WHY???? Come on down and get some base pairs

CHM 112 M. Prushan The Guanine-Cytosine (GC) Base Pair

CHM 112 M. Prushan The Guanine-Cytosine (GC) Base Pair

CHM 112 Summer 2007 M. Prushan Effect of Intermolecular forces on melting and boiling points of molecular covalent substances Increase only due to increase in MW, Since all are non-polar 16 32 77 132 Molecular wts. 20 37 81 128 Why does HF have the highest BP? Molecular wts. BONDS… Hydrogen Bonds

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