Intermolecular forces 2012

Intermolecular forces 2012 - Intermolecular Intermolecular...

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Intermolecular Forces David A. Katz Department of Chemistry Pima Community College
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States of Matte States of Matter The fundamental difference between states of matter is the distance between particles.
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States of Matte 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 •T h e s t a t e a s u b s t a n c e i s in at a particular temperature and pressure depends on two antagonistic entities – The kinetic energy of the particles –T h e s t r e n g t h o f t h e attractions between the particles
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Intermolecular Forces The attractions between molecules are not nearly as strong as the intramolecular nearly as strong as the intramolecular attractions that hold compounds together.
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Intermolecular Forces They are, however, strong enough to control physical properties such as boiling and physical properties such as boiling and melting points, vapor pressures, viscosities, surface tension, and related properties.
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Intermolecular Forces These intermolecular forces as a group are referred to as van der Waals forces referred to as .
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Intermolecular Forces •L o n d o n d i s p e r s i o n f o r c e s •D i p o l e - i n d u c e d d i p o l e i n t e r a c t i o n s • Dipole-dipole interactions Dipole dipole interactions •H y d r o g e n b o n d i n g • Ion-induced dipole interactions •I o n - d i p o l e i n t e r a c t i o n s
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London Dispersion Forces While the electrons in the 1 s orbital of helium would repel each other (and, although they are paired tend to stay away from each are paired, tend to stay 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 and a shortage on the right side. This is called an instantaneous dipole
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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. The second helium atom has an induced dipole
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London Dispersion Forces London dispersion forces, or dispersion forces are attractions between an forces, are attractions between an instantaneous dipole and an induced dipole.
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London Dispersion Forces •T h e s e f o r c e s a r e p r e s e n t i n all molecules, whether they are polar or nonpolar. h e t e n d e n c y o f a n e l e c t r o n c l o u d t o d i s t o r t i n this way is called polarizability .
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Factors Affecting London Forces The shape of the molec le • The shape of the molecule affects the strength of dispersion forces: long skinny molecules
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Intermolecular forces 2012 - Intermolecular Intermolecular...

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