Ch 11 - Ch 11 Liquids Solids(11.2 11.3 11.5-11.8 A 11.3...

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Ch. 11 Liquids + Solids (11.2, 11.3, 11.5-11.8) A. 11.3 Intermolecular Forces (IMFs) a. IMFs = forces that occur between 2+ molecules (what forces attract the molecules) b. inTRAmolecular forces : occur within one molecule (like ionic bonding, polar- covalent and non-polar covalent bonding) b.i. For molecule AB b.i.1. A—B (intra); AB….AB (inter) c. Two types: (depending on how A and B are polarized) c.i. dipole-dipole forces (including H-bonds) c.i.1. The A—B bond has a permanent dipole c.ii. London dispersion forces c.ii.1. A—B has a temporary dipole c.ii.1.a. (δ+) A—B (δ-) - - - - - - (δ+) A—B (δ-) c.ii.2. present in all molecules + atoms c.ii.3. are the result of fluctuations in electron distribution within molecules/atoms c.ii.3.a. at any ONE instant may be unevenly distributed, making one side slightly more positive/negative than other c.ii.3.b. this is called an instantaneous dipole or temporary dipole c.ii.3.c. the instantaneous dipole then induces instantaneous dipole of neighboring atom c.ii.4. magnitude of dispersion force depends on how easily the electrons in atom/molecule can move or polarize in response to an instantaneous dipole, which depends on size/volume of electron cloud c.ii.4.a. larger MM, the greater the electron cloud, the greater the dispersion forces since larger cloud means electrons are held less tightly by nucleus and thus can be polarized more c.ii.4.b. flatter SA also d. Strength of Inter- and Intramolecular Forces d.i. Intra are much stronger (important to keep molecules together) Force Inter or Intra Strength kJ/mole Ionic bond Intra 400 - 500 Covalent bond Intra 100 - 400 H-bond Inter 4 - 50 Dipole-dipole Inter 5 - 20 London force inter 1.1 5 e. Coulomb’s Law + IMFs e.i. intermolecular forces are weak since they involve partial charges on molecules e.ii. there are large distances (r) between molecules e.ii.1. Coulomb’s law: E e.iii. strength of IMFs determine phase:
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e.iii.1. solids have STRONG IMFs e.iii.2. liquids have moderate IMFs e.iii.3. gases (ideally) have no IMFs f. Dipole-dipole forces f.i. dipole-dipole forces —when polar molecules approach each other, their partial charges act as small electric fields f.i.1. exists in all molecules that are polar f.i.1.a. polar molecules have permanent dipoles that interact with permanent dipoles of neighboring molecules f.i.1.b. add’l force increases melting + boiling points of nonpolar molecules f.i.2. one molecule’s positive pole attracts negative pole of another f.i.3. red = δ- blue = δ+ f.i.4. HF can hydrogen bond, so is stronger than HI (which has higher MW, which usually is stronger) B. 11.3 Hydrogen Bonding a. strong dipole-dipole occurs in molecules with H bonded to N, O, F a.i. N O F only H-bond because a.i.1. they are small molecules—can approach closely a.i.1.a. very EN—strong partial charges on H and N/O/F a.i.1.b. the H induces attraction to N/O/F of other molecules a.ii. is an intermolecular force, occurs between molecules
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This note was uploaded on 02/17/2012 for the course CHEM 105ALg taught by Professor Bau during the Spring '07 term at USC.

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Ch 11 - Ch 11 Liquids Solids(11.2 11.3 11.5-11.8 A 11.3...

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