chapter_11au_1

chapter_11au_1 - Chapter 11 Intermolecular Forces, Liquids,...

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Intermolecular Forces Chapter 11 Intermolecular Forces, Liquids, and Solids
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Intermolecular Forces States of Matter The fundamental difference between states of matter is the distance between particles. condensed phases
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Intermolecular Forces The States of Matter The state a substance is in at a particular temperature and pressure depends on two opposing entities: The kinetic energy of the particles (Temperature) The strength of the attractions between the particles (Intermolecular forces) a. b. c. d. a. b. c. d. a. b. c. d. KE>IF IF>KE IF KE
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Intermolecular Forces Intermolecular Forces The attractions between molecules are not nearly as strong as the intramolecular attractions that hold compounds together. They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities. These intermolecular forces as a group are referred to as van der Waals forces .
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Intermolecular Forces Covalent vs. intermolecular forces Covalent bond Intermolecular forces Attractive -1/R n R (distance) P o t e n i a l r g
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Intermolecular Forces Ion-Dipole and ion –ion Interactions: involved charged particles Ion-ion ( ± 1/R) and ion-dipole interactions (attractive) are important forces in solutions of ions. The strength of ion-dipole forces are what make it possible for ionic substances to dissolve in polar solvents.
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Intermolecular Forces van der Waals Forces Between neutral molecules Fall off as -1/R 6 (Coulomb falls as ± 1/R) Three types Dipole-dipole interactions London dispersion forces Hydrogen bonding
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Intermolecular Forces Dipole-Dipole Interactions Molecules that have permanent dipoles are attracted to each other (-1/R 6 ). The positive end of one is attracted to the negative end of the other and vice-versa. These forces are only important when the molecules are close to each other.
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Intermolecular Forces Dipole-Dipole Interactions The more polar the molecule, the higher is its boiling point.
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Intermolecular Forces London Dispersion Forces: induced dipole While the electrons in the 1 s orbital of helium would repel each other (and, therefore, tend to stay far away from each other), it does happen that they occasionally wind up on the same side of the atom. At that instant, then, the helium atom is polar, with an excess of electrons on the left side and a shortage on the right side.
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Forces London Dispersion Forces Another helium nearby, then, would have a dipole induced in it London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole (instant dipole-induced dipole) These forces are present in all molecules, whether they are polar or nonpolar. The tendency of an electron cloud to distort in this
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This note was uploaded on 10/22/2011 for the course CHEM 1111 taught by Professor Ramaker during the Fall '10 term at GWU.

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chapter_11au_1 - Chapter 11 Intermolecular Forces, Liquids,...

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