ChemReview4 - Intramolecular Forces: forces that hold...

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molecular Forces: forces that hold together an individual molecule Stronger than intermolecular Inter molecular Forces: forces between individual molecules in a chemical sample Molecules remain intact. Changes occur among the molecules rather than within. Dipole-dipole forces o Hydrogen bonding F, O, N Great polarity of the bond Close approach of the dipoles owing to the small size of the hydrogen atom. London Dispersion Forces—London dispersion forces or van der Waals forces o London forces exist in ALL molecules but are the ONLY form of interaction in nonpolar molecules and noble gases. Ion-ion interactions Intermolecular forces based on attraction of opposite charges o Electrostatic Forces In covalent molecules, intermolecular forces are based on the molecule polarity A molecule that is polar overall will have a NET DIPOLE moment. Stronger Intermolecular interactions: Means it is harder to SEPARATE the component atoms/ions Means higher melting and boiling points Surface Tension is an inward force that acts against a liquid’s surface area from expanding. For a surface to expand, molecules must move to the surface, which takes energy to overcome intermolecular forces Capillary Action- Polar liquids also exhibit capillary action, the spontaneous rising of a liquid in a narrow tube. Two types of forces are responsible for this property: o COHESIVE FORCES : hold liquid together o ADHESIVE FORCES : hold liquid to another surface Liquid water creeps up sides of tube until limited by gravity. Roots use this! Adhesive force is stronger than cohesive force in this case! For non-polar mercury, cohesive forces are stronger than adhesive forces toward the glass and a convex meniscus is formed. Viscosity
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This note was uploaded on 01/30/2012 for the course CHEM 301 taught by Professor Wandelt during the Spring '08 term at University of Texas at Austin.

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ChemReview4 - Intramolecular Forces: forces that hold...

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