Chapter11-all-MRC

Chapter11-all-MRC - Chapter 11 Intermolecular Forces...

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Chapter 11 Intermolecular Forces, Liquids, and Solids
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States of Matter The fundamental difference between states of matter is the distance between particles.
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States of Matter Because in the solid and liquid states particles are closer together, we refer to them as condensed phases.
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The States of Matter The state a substance is in at a particular temperature and pressure depends on two antagonistic entities: The kinetic energy of the particles The strength of the attractions between the particles
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Inter- and Intra-molecular Forces The attractions between molecules (intermolecular) are not nearly as strong as the intra-molecular attractions that hold compounds together.
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Intermolecular Forces They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities.
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Intermolecular Forces These intermolecular forces as a group are referred to as van der Waals forces .
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van der Waals’ Forces Four types of van der Waals’ Forces Ion-Dipole interactions Dipole-dipole interactions London dispersion forces Hydrogen Bonding
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Ion-Dipole Interactions Ion-dipole interactions are an important force in solutions of ions. The strength of these forces are what make it possible for ionic substances to dissolve in polar solvents.
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Dipole-Dipole Interactions Molecules that have permanent dipoles are attracted to each other. 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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Dipole-Dipole Interactions The more polar the molecule, the higher is its boiling point.
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London Dispersion Forces 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.
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London Dispersion Forces 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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London Dispersion Forces Another helium nearby, then, would have a dipole induced in it, as the electrons on the left side of helium atom 2 repel the electrons in the cloud on helium atom 1.
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London Dispersion Forces London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole.
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London Dispersion Forces These forces are present in all molecules, whether they are polar or nonpolar. The tendency of an electron cloud to distort in this way is called polarizability.
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The shape of the molecule affects the strength of dispersion forces: long, skinny molecules (like n - pentane tend to have stronger dispersion forces than short, fat ones (like neopentane).
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This note was uploaded on 04/29/2008 for the course CHE 101 taught by Professor Churchhill during the Spring '08 term at SUNY Buffalo.

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Chapter11-all-MRC - Chapter 11 Intermolecular Forces...

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