Bonds & IMAFs in Liquids, Solids, and Solutions

Transcription

1 Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Unit 5 (Chp 11,13) Bonds & IMAFs in Liquids, Solids, and Solutions John D. Bookstaver St. Charles Community College St. Peters, MO 2006, Prentice Hall, Inc. Bonds Intra (strong) Attractions IMAFs Inter (weak) Ionic (metal nonmetal) Covalent (nonmetals) polar nonpolar??? Intermolecular Attractive Forces Intramolecular Attraction (within) (strong bonds) (weak) Intermolecular Attraction (between) Which attraction is overcome (broken) by melting & vaporizing? weak IMAFs between molecules 1

2 Intermolecular Attractive Forces Intramolecular Attraction (within) (strong bonds) (weak) Intermolecular Attraction (between) IMAFs determine physical properties such as boiling & melting points, bp, mp, vapor pressure, and viscosity. vp, visc. States of Matter The main difference between phases of matter is the distance between particles. changes of state States of Matter State (distance between particles) at a certain T and P depends on two opposing qualities: KE (kinetic energy of the particles vs. IMAFs (intermolecular attractive forces between particles) 2

3 Bonds Intra (strong) Attractions IMAFs Inter (weak) Ionic (metal nonmetal) Covalent (nonmetals) polar nonpolar? London Dispersion Forces Electrons in the 1s orbital of He repel each other, BUT they occasionally wind up on the same side of the atom. δ δ + At that instant, the He atom is polar (instantaneous dipole). (excess of e s on one side, and shortage on the other) London Dispersion Forces causes induced dipole instantaneous dipole δ δ + δ δ + LDFs: attractions between instantaneous dipoles and induced dipoles caused by motion of e s. 3

4 London Dispersion Forces δ δ + δ δ + present in all molecules, (polar & nonpolar) The tendency of an electron cloud to distort to become temporarily polar in this way is called. polarizability Factors Affecting London Forces MW (molecular weight) LDFs increase with increased MW b/c larger e clouds, are more polarizable. (use this phrase to answer FR question) Factors Affecting London Forces Shape long, skinny molecules have stronger IMAFs due to increased surface area to form more attractions. (SA cylinder > SA sphere ) 4

5 Bonds Intra (strong) Attractions IMAFs Inter (weak) Ionic (metal nonmetal) Covalent (nonmetals) polar nonpolar London dispersion forces (nonpolar & all)? Dipole-Dipole Interactions (dipole) (dipole) Polar molecules with permanent dipoles are attracted to each other. Dipole-Dipole Interactions? EN polar bonds assym. shape The more polar the molecule, the higher the boiling/melting point. (due to greater dipole-dipole IMAFs that require more energy to overcome) 5

6 Which Have a Greater Effect: Dipole-Dipole Interactions or Dispersion Forces? dipole dipole interactions (permanent dipoles) are typically stronger than LDFs (temporary dipoles as instantaneous induced). But much larger molecules could have LDFs that are stronger than dipole-dipole interactions. (larger e clouds, are more polarizable) Bonds Intra (strong) Attractions IMAFs Inter (weak) Ionic (metal nonmetal) Covalent (nonmetals) polar nonpolar London dispersion forces (all, nonpolar) dipole dipole (polar)? How Do We Explain This? Boiling Points unusually high bp unusually strong IMAFs polar nonpolar 6

7 Hydrogen Bonding H-bonds are caused by an electron deficient H atoms (bonded to N, O, or F) attracted to small, very electronegative N, O, or F atoms on a nearby molecule. Bonds Intra (strong) Attractions IMAFs Inter (weak) Ionic (metal nonmetal) Covalent (nonmetals) polar nonpolar London dispersion forces (all, nonpolar)? dipole dipole (polar) H bonds H with N, O, F Ion-Dipole Interactions ionic solutes dissolve in polar solvents H O H Na + Cl H O H 7

8 Bonds Intra (strong) Attractions IMAFs Inter (weak) Ionic (metal nonmetal) Covalent (nonmetals) polar nonpolar London dispersion forces (all, nonpolar) ion dipole (aq ions) dipole dipole (polar) H bonds H with N, O, F Stronger Weaker HW (ion dipole) p. 476 #1 Intermolecular Attractive Forces (ion dipole) H-bonds (if H with N, O, or F) dipole-dipole int. s (polar molecules) London dispersion forces (nonpolar, instant induced dipoles) Organic Functional Groups Alkanes London dispersion forces (LDFs) only bp increases as length of chain b/c larger e cloud, more polarizable 8

9 Organic Functional Groups What IMAFs? polar & H-bond polar Organic Functional Groups What IMAFs? polar & H-bond polar polar polar & H-bond butane (alkane) LDFs dipole-dipole ethylamine (amine) H-bond dipole-dipole 3 pentanone (ketone) H-bond trimethylamine (amine) H-bond ethanol (alcohol) dipole-dipole ethanoic acid (carboxylic acid) propanal (aldehyde) 9

10 IMAFs in Protein Structure & DNA acid amino protein IMAFs in Protein Structure & DNA hold, but can be broken HW p. 476 #2-26 Intermolecular Forces Affect Many Physical Properties The strength of the attractions between particles can greatly affect the physical properties of a substance or solution. 10

11 Cohesive/Adhesive Forces Adhesive to surface Cohesive to each other glass adhesive cohesive Capillary Action due to co/adhesive forces 11

12 results from the net inward force experienced by the molecules on the surface of a liquid. Surface Tension Viscosity resistance of a liquid to flow increases with IMAF s and decreases with higher temp. HW p. 479 #29 Phase Changes HW p. 479 #34 12

13 Energy and Phase Changes Heat of Fusion (H fus ): energy to change (s) to (l) at melting point. Energy and Phase Changes DEMO: butane Heat of Vaporization (H vap ): energy to change (l) to (g) at boiling point. Energy and Phase Changes What happens to added KE? Temp. does not change during phase change. HW p. 480 #35, 47a Added energy separates particles (overcome IMAFs) ( PE) 13

14 Vapor Pressure pressure above liquid more volatile = more vapor = weak IMAFS liquid molecules escape to vapor gas molecules condense to liquid (dynamic equilibrium) Vapor Pressure As T, the fraction of molecules that have enough energy to escape increases. Vapor Pressure As more molecules escape the liquid, the pressure they exert increases. Dynamic Equilibrium: vaporize/condense at same rate 14

15 normal b.p.: T at which v.p. = 1 atm boiling point: T at which vapor pressure = atmospheric pressure Vapor Pressure DEMO: boil H 2 O HW p. 480 #47b, 48 Solutions + homogeneous mixtures of pure substances. solute is dispersed uniformly throughout the solvent. Why does stuff dissolve? IMAFs between solute solute solvent solvent IMAFs between solute solvent must be stronger solvated (dissolved) 15

16 For Ionic Solutes Ions are soluble in water because ion-dipole attractions are strong enough to overcome the crystal lattice energy of the ionic solid salt. Energy Changes in Solution separation of solute separation of solvent (absorb = endothermic) (absorb = endothermic) attractions between solute and solvent (release = exothermic) Demo Calcium Chloride CaCl 2 feels warmer Ammonium Chloride NH 4 Cl feels cooler Heat flows where? into or out of? into or out of? 16

17 + + + H enthalpy (heat) H (final initial) + + Why Do Endothermic Processes Occur? Usually favorable processes tend to lower energy. E = (exo or release) But in some processes, heat is absorbed, not released. How? Entropy Entropy (S): dispersal of matter & energy increasing the entropy (dispersal) ( S = +) by mixing lowers the energy ( E = ) of a system (even if H = +). (less dispersal) S = (final initial) S = (more less) S = + (more dispersal) + H (absorb heat)(+ E) + S (gain entropy)( E) E + E (lowered) (raised) 17

18 Types of Solutions Unsaturated Less than the maximum dissolved at that temperature. Types of Solutions Saturated Solvent holds maximum solute possible at that temperature. Dissolved solute is in dynamic equilibrium with solid solute particles. Types of Solutions Supersaturated More solute than is normally possible at that temperature. unstable; crystallization is stimulated by a seed crystal or scratching. 18

19 Factors Affecting Solubility like dissolves like : (similar IMAFs) Polar substances dissolve in polar solvents. H 2 O CH 3 Cl CH 3 CH 2 OH NH 3 Nonpolar dissolve in nonpolar solvents. C 6 H 14 CCl 4 I 2 similar IMAFs are more soluble. HW p. 566 #12,14,18 Which is more soluble in water (H 2 O) and which is more soluble in hexane (C 6 H 14 ) Gases in Solution In general, the solubility of gases in water increases with increasing size. WHY? Larger molecules have larger e clouds stronger dispersion forces. 19

20 Gases in Solution The solubility of gas in liquid is directly proportional to pressure. Gases are more soluble: Low T High P solubility of solids inc. with temp. Solubility Curves HW p. 566 #20,23,25 1) Highest solubility at 20 o C? 30 o C? 2) How many grams KClO 3 at 70 o C? 3) Is 50 g of KCl at 50 o C sat, unsat, or supersat? 30 g of NaCl at 30 o C? Intermolecular Forces Affect Many Physical Properties The greater the IMAFs, the greater the bp and mp. the greater the cohesion/adhesion. the greater the surface tension. the greater the viscosity. the lower the vapor pressure (volatility) 20

21 Intermolecular Forces Affect Many Physical Properties Which has a higher boiling point? Explain. CF 4 vs. CH 3 OCH 3 CF 4 has London dispersion forces and CH 3 OCH 3 has dipole-dipole interactions. Stronger intermolecular attractive forces in CH 3 OCH 3 require more energy to overcome. mp s (of solids) Bonds Intra (strong) Attractions mp s & bp s IMAFs Inter (weak) Ionic (metal nonmetal) Covalent (nonmetals) polar nonpolar London dispersion forces (all, nonpolar) dipole dipole (polar) ion dipole (aq ions) H bonds H with N, O, F 4 Types of Bonding in Solids Ionic [metal nonmetal] transfer e s forming attractive charged ions Diamond Covalent [nonmetals] sharing e s in mutual nuclear attraction Covalent Network [C (d) ] shares e s throughout Quartz Metallic [metals] metal atoms bonded by delocalized val. e s 21

22 Ionic Solids more q less d stronger attraction more energy to break (ordered) Strong Ionic Bonds in a crystal lattice of +/ ions bonded by electrostatic attraction. hard and brittle (Coulombic) high melting points E = κ q 1q 2 d conduct in solution(aq) or molten(l) Covalent (Molecular) Solids C (graphite) Weak IMAF s (LDF s, dipole-dipole, H-bonds) softer lower melting points Covalent-Network Solids C (graphite) C (diamond) Strong Covalent Bonds throughout. C (diamond) WC 2 (carbide) SiO 2 (quartz) Very hard Very high melting points 22

23 Metals are not covalently bonded, but attractions are too strong to be IMAFs. Metallic Solids Metallic Bonds delocalized valence sea of electrons. Excellent conductors Malleable and Ductile ( smooshable ) soft to very hard low to very high m.p. s Brass Alloys Steel 67%Cu, 33%Zn 80%Fe, 0.4%C, 18%Cr, 1%Ni Alloys: Homogeneous metallic mixtures (solutions) by mixing melted metals in the liquid phase. Attractions: Held together mainly by metallic bonding due to a delocalized sea of electrons. Brass Alloys Steel C Fe Fe Fe Fe Fe Fe Fe Substitutional: at. radius: similar density: in between malleability: similar Fe Fe Fe Fe Interstitial: at. radius: different (smaller fits between larger) density: greater (more mass in same volume) malleability: less (harder) 23

24 Attractions in Solids, Liquids, & Solutions Ar I 2 CO 2 H 2 O C 2 H 5 OH C 11 H 22 O 11 C (diamond) SiO 2 WC 2 NaCl CuSO 4 Type Forces Between Particles Properties Intermolecular Attractions(IMAFs) Molecular London dispersion forces (nonpolar) Dipole-dipole interactions (polar) δ δ + Covalent- Network Ionic (l) + (l), Solutions (s) + (l) = (aq) Hydrogen bonds(h with N, O, F) Covalent Bonds(network) C (diamond), SiO 2 (quartz), WC 2 (tungsten carbide), etc Ionic Bonds crystal lattice of charged ions Metallic Bonds + q 1 q 2 d All metals Metallic delocalized sea of val.e & alloys: Cu, Fe, K, Al, s Solute-Solvent Attractions similar IMAFs or ion dipole Soft Low mp & bp Poor conductor Very hard Very high mp Poor conductor Hard and brittle High mp Conducts as (aq) or (l) Soft to very hard Low to very high mp Conductor, Malleable, Ductile Attraction or Bond Molecular (IMAFs) Hydrogen bonds (if H with N, O, or F) Dipole-dipole interactions (polar molecules) London dispersion forces (all molecules & nonpolar) instant/induced dipoles) Ionic Bonds (attractions between +/ ions) Stronger with: greater EN N < O < F greater EN greater dipole moment larger e cloud, more polarizable greater q, less d (Coulombic attraction) The Stronger the Attractions, the higher mp of solid (higher H fus ) harder solid Attractions Affect Physical Properties higher bp of liquid (higher H vap ) higher viscosity of liquid lower vapor pressure of liquid (more volatile) more soluble (similar solute-solvent IMAFs) 24

25 Reasoning with Concepts 1) Identify attractions (Bonds? IMAFs?) 2) Compare strength + 3) Connect to energy (abs./rel.) and/or physical property 25