Class08

Class08 - Formation and Nature of the Hydrosphere...

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Unformatted text preview: Formation and Nature of the Hydrosphere Hydrosphere refers to the water portions of earth (oceans, lakes, rivers, etc) There are two types of forces associated with molecules http://www.miramar.sdccd.cc.ca.us/faculty/fgarces/ChemProj/Ch201_Sp2001/Margarita/IMF.htm Intramolecular forces- strong forces (50-1000 kcal/mole) between atoms within a molecule. Determine chemical properties. Intermolecular forces- weak forces (0.05-40 kcal/mole) between two different molecules. Determine physical properties. Van der Waals Force has three components: LDF, DDF, and H-bonding. Strong covalent bond, 103 kcal/mole Weak Van der Waals Force, 4 kcal/mole London Dispersion Force (LDF) • As two molecules approach each other, the attractions and repulsions between their nuclei and electrons cause distortions of their electron arrangements producing temporary electric dipoles that attract each other http://www.lakelandschools.us/lh/lburris/pages/bonds.htm Non-polar molecules approaching each other LDF is the force of attraction between the resulting temporary fluctuating dipoles Mutual distortion http://bdml.stanford.edu/twiki/pub/Rise/InvestigationOfVanDerWaalsForce/image002.png A temporary dipole can induce a temporary dipole in an adjacent molecule. London Dispersion Force , LDF, is the force of attraction between opposite charges of adjacent temporary dipoles Induction disperses throughout all adjacent molecules resulting in LDF between all molecules in a sample LDF LDF is exhibited by all molecules and ranges from 0.01 - 10 kcal/mole, depending on SIZES and SHAPES of molecules. Trends in London Dispersion Forces (LDF) Prentice Hall 2003, Chp 11 Size increases LDF increases LDF increases Size increases SIZE : LDF increases as sizes of molecules increase , since there are more electrons and they are located further from their nuclei. **BP is used as a semi-quantitative indicator of the forces of attraction between molecules since molecules must move faster to overcome an intermolecular force. *Molecular weight is used as a semi-quantitative indicator of sizes of molecules. ** * http://itl.chem.ufl.edu/2041_f97/matter/FG11_006.GIF BP = 36 o C BP = 10 o C Less atoms in close proximity in adjacent molecules SHAPE : LDF increases with those shapes of molecules that increase the number of atoms that can be in close proximity as two molecules approach each other (exposable surface area). Stronger LDF - more opportunity for mutual distortion of electron locations Two structures for C 5 H 12 Dipole-Dipole Force (DDF) http://wine1.sb.fsu.edu/chm1045/notes/Forces/intermol/Forces02.htm Permanent dipoles result from differences in EN of atoms in a molecule. DDF is the force of attraction between permanent dipoles of adjacent polar molecules DDF is exhibited only by polar molecules, and is 1 - 6 kcal/mole in magnitude DDF Prentice Hall 2003, Chp 11 Trend in Dipole-Dipole Force (DDF) Size roughly constant Polarity increases BP increases **BP is used as a semi-quantitative indicator of the forces of attraction...
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This note was uploaded on 10/19/2011 for the course CHEM 83 taught by Professor Bonk,j during the Fall '08 term at Duke.

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Class08 - Formation and Nature of the Hydrosphere...

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