chap10notes - Chapter 10 Liquids and Solids 10.1...

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1 Chapter 10 - Liquids and Solids 10.1 Intermolecular Forces A. Dipole-Dipole Forces 1. Attraction between molecules with dipole moments a. Maximizes (+) ----- ( - ) interactions b. Minimizes (+) ----- ( + ) and (-) ----- ( - ) interactions 2. About 1% of strength of ionic bonds a. Unimportant in gas phase due to distance between molecules B. Hydrogen Bonding 1. Special dipole-dipole attraction a. Hydrogen covalently bonded to highly electronegative elements (N, O, F) has a higher than normal δ + charge 2. Bond strength is higher than other dipole-dipole attractions 3. Important in the bonding of molecules such as water and DNA C. London Dispersion Forces 1. Instantaneous dipoles a. Random movement of electrons can create a momentary nonsymmetrical distribution of charge even in nonpolar molecules b. Instantaneous dipoles can induce a short-lived dipole in a neighboring molecule 2. London dispersion forces exist between all molecules, but are the weakest forces of attraction 3. "Polarizability" increases with the number of electrons in a molecule a. CCl 4 experiences greater London forces than CH 4 10.2 The Liquid State A. Surface Tension 1. The resistance of a liquid to an increase in its surface area 2. High intermolecular forces greater high surface tension B. Capillary Action 1. Cohesive forces between liquid molecules 2. Adhesive forces between polar liquid molecules and polar bonds in the material making up the container a. Water's adhesive forces are greater than its cohesive forces, thus the increase in surface area (concave meniscus) b. Oxygen in glass is attracted to hydrogen in water C. Viscosity 1. Measure of a liquid's resistance to flow a. Viscosity increases with intermolecular forces b. Viscosity increase with molecular size D. Structural Model for Liquids 1. Strong intermolecular forces (like solids) 2. Considerable molecular motion (like gases)
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2 10.3 An Introduction to Structures and Types of Solids A. Types of solids 1. Crystalline solids a. Highly regular arrangement of components b. Components organized in a three-dimensional lattice (1) Smallest repeating unit of the lattice is a unit cell 2. Amorphous solids a. Components "frozen in place" and lacking orderly arrangement (1) glass (2) plastic B. X-ray Analysis of Solids 1. Structure of crystalline solids can be determined by xray diffraction a. waves in parallel beams that are "in phase" produce constructive interference b. waves in parallel beams that are "out of phase" produce destructive interference q = angle of incidence and reflection d = distance between atoms n = integer l = wavelength 2. Bragg's Law
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