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Unformatted text preview: Chapter 16 Objectives
16.1 Describe the differences between intermolecular and intramolecular forces with an emphasis on the relative energies of each type of attraction. 16.2 Discuss the influence of these forces on physical properties such as freezing point and boiling point. 16.3 Provide real-life applications with biological systems such as DNA or proteins, and other systems as appropriate. 9/28/2008 Zumdahl Chapter 16 1 Intermolecular Forces: Why Condensed Phases Exist Intramolecular Forces, i.e., Chemical bonds Intramolecular Strong Directional Short Range (relative) Intermolecular Forces Intermolecular Weaker than chemical bonds, usually much weaker Less directional than covalent bonds, more directional than ionic bonds ionic Longer range than covalent bonds but at shorter range than ionic bonds Condensed Phases Solids and Liquids Intermolecular forces: Mutual attractions hold the molecules closer Intermolecular forces: together than gases
Zumdahl Chapter 16 2 9/28/2008 1 Types of Intermolecular (Non-bonding) Interactions 9/28/2008 Zumdahl Chapter 16 3 Dipole - Dipole Interactions and Hydrogen Bonding What is a hydrogen bond? A particularly strong dipole-dipole interaction where hydrogen is dipole- "bound" to a highly electronegative second row atom, i.e., N, O, or bound" F. The strength of the interaction results from the great polarity of polarity the bond and the closer than normal approach of the dipoles.
9/28/2008 Zumdahl Chapter 16 4 2 The Boiling Points of the Covalent Hydrides of Elements in Groups 4A, 5A, 6A, and 7A. 9/28/2008 Note Importance of Hydrogen Bonding Zumdahl Chapter 16 5 Ion - Dipole Interactions 9/28/2008 Zumdahl Chapter 16 6 3 Ion - Induced Dipole Interactions
Ar Ar 9/28/2008 Zumdahl Chapter 16 7 London Dispersion Forces 9/28/2008 Zumdahl Chapter 16 8 4 Kinetic Theory of Liquids and Solids Intermolecular distances Intermolecular Solids about 3 X 10 -10 m = Liquids about 5 X 10 -10 m = Gases: much larger than liquids unless P > 100 atm Intramolecular bonds Intramolecular
Zumdahl Chapter 16 9/28/2008 9 The Liquid State
Characteristics of the Liquid State
Low compressibility High density, relative to gases Surface tension Exhibit capillary action Cohesive forces Adhesive forces Viscosity water is "thin", having a lower viscosity vegetable oil is "thick" having a higher viscosity. 9/28/2008 Zumdahl Chapter 16 10 5 A molecule in the interior of a liquid is attracted to the molecules molecules surrounding it, whereas a molecule at the surface of liquid is attracted only by molecules below it and on each side of it.
bind molecules of the same type together bind a substance to a surface 9/28/2008 Zumdahl Chapter 16 11 Adhesive Forces and Capillary Action X Concave Meniscus Convex Meniscus
Example: Example: X X X X X X x 9/28/2008 Zumdahl Chapter 16 12 6 Introduction to Structures and Types of Solids Highly regular arrangement "Lattice": 3D arrangement, with unit cell structures Lattice" Simple cubic (Po metal) Body-centered cubic (Ur metal) Face-centered cubic (Au metal) Disordered structures Non-crystalline Non E.g., window glass
9/28/2008 Zumdahl Chapter 16 13 Three cubic unit cells and the corresponding lattices 9/28/2008 Zumdahl Chapter 16 14 7 X-rays scattered from two different atoms may reinforce (constructive interference) or (constructive interference) cancel (destructive interference) one another (destructive interference) d = =
9/28/2008 Zumdahl Chapter 16 15 Reflection of X rays
Bragg Equation 9/28/2008 Zumdahl Chapter 16 16 8 Examples of Three Types of Crystalline Solids
Atomic Solids Ionic Solids Molecular Solids 9/28/2008 Zumdahl Chapter 16 17 In te r a c tin g m o le c u le s o r io n s C o n s id e r th e c o m p o s itio n , e lc e tr o n e g a tiv ie s a n d s tr u c tu re o f th e s p e c ie s P le a s e a ls o re v ie w C h a p te r 1 3 s u c h c o n c e p ts a s io n s , io n ic , c o v a le n t b o n d in g a n d d ip o le m o m e n ts NO A r e p o la r m o le c u le s in v o lv e d ? NO A re io n s in v o lv e d ? YES A re p o la r m o le c u le s a n d io n s p r e s e n t? NO Y E S (D ip o le - D ip o le in te r a c tio n s ) A re h y d ro g e n a to m s b o n d e d to N , O , o r F a to m s ? YES YES NO D is p e rs io n fo r c e s o n ly (in d u c e d d ip o le s ) E x a m p le s : A r ( l) , I2 (s ) D ip o le -D ip o le fo rc e s E x a m p le s : H 2S , C H 3C l H y d r o g e n B o n d in g (s p e c ia liz e d ty p e o f d ip o le -d ip o le ) E x a m p le s : liq u id a n d s o lid H 2 O , N H 3, H F Io n -D ip o le fo rc e s E x a m p le s : K B r in w a te r Io n ic B o n d in g E x a m p le s : N a C l, N H 4 N O 3 V a n d e r W a a ls fo r c e s h ig h e s t S t r e n g t h o f In te r s p e c ie s F o r c e s G e n e r a lly In c r e a s e s fr o m L e f t t o R ig h t
N o te s 1 . D is p e rs iv e fo rc e s a r e fo u n d in a ll s u b s ta n c e s . T h e s tre n g th o f d is p e r s iv e fo r c e s in c r e a s e s w ith M o la r M a s s . 2 . D ip o le -D ip o le fo r c e s a d d to th e e ffe c t o f d is p e rs iv e fo rc e s a n d a r e fo u n d in p o la r m o le c u le s . 3 . H y d r o g e n b o n d s , w h ic h re q u ire H a to m s b o n d e d to F , O , o r N , a ls o a d d to th e e ffe c t o f d is p e r s io n fo r c e s . H y d r o g e n b o n d s te n d to b e th e s tr o n g e s t ty p e o f in te r m o le c u la r fo r c e s . 4 . O rd in a r y Io n ic (a n d c o v a le n t) b o n d in g fo r c e s a r e th e s tro n g e s t. 9/28/2008 Zumdahl Chapter 16 18 9 Chapter 16 Liquids and Solids
16.1 Intermolecular Forces 16.2 The Liquid State 16.3 An Introduction to Structures and Types of Solids 16.4 Structure and Bonding in Metals 16.5 Carbon and Silicon: Network Atomic Solids 16.6 Molecular Solids 16.7 Ionic Solids 16.8 Structures of Actual Ionic Solids 16.9 Lattice Defects 16.10 Vapor Pressure and Changes of State 16.11 Phase Diagrams 9/28/2008 Zumdahl Chapter 16 19 10 ...
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