chem101/3, wi2010 po 20 1 States of Matter SM VI Description of Liquids & Solids chem101/3, wi2010 po 20 2 Liquids molecules slide along in close contact attraction due to various IMF s can diffuse, but much slower than gases Kinetic Energy & Molecular Speeds (analogous to gases) for 1 mol: KE = 3 2 R T Ref Prob 12: 4, 6 (selected) memorize types of solids, examples, properties speed distribution (depends on MM, T) ΔN u /N Adv Rdg 12: 2 u chem101/3, wi2010 po 20 3 Macroscopic Properties Can ignore in 2010 Must know definitions (for more details consult Pet.12.1) chem101/3, wi2010 po 20 4 Vapor Pressure must remember! review HT lecture 15:19-22 viscosity: resistance to flow (re)do textbook problems surface tension: resistance to surface increase capillarity: interaction between liquids and solid surfaces cohesive forces refer: to interaction between molecules in liquid note especially: if IMF then VP, b.p. adhesive forces refer to interaction between liquid molecules & solid surface if adhesive forces stronger than cohesive: get concave meniscus if cohesive forces stronger than adhesive: get convex meniscus All depend on IMF s
chem101/3, wi2010 po 20 5 Solids have no translational mvmt chem101/3, wi2010 po 20 6 Solids... B.) Crystalline vibrate in fixed position Distinguish 2 types of arrangements: A.) Amorphous ( = w/t shape, also: non-crystalline) molecules arranged randomly ( no nice repeating pattern) amorphous have highly organized structure w/ fixed repeating pattern Examples: diamond, C table salt, NaCl table sugar, C 12 H 22 11 random arrangement uranium, metal, U often obtained by fast cooling (supercooling) of liquids Ex. Window Glass chem101/3, wi2010 po 20 7 Classification of Crystalline Solids acc. to IMF s chem101/3, wi2010 po 20 8 1.) Molecular Solids 3 D pattern maintained by IMF s Class of Solid Attractive Force Examples: 1.) molecular various IMF s (dipole-dipole, H-Bonding, LDF s...) substance 1.) ice, H 2 (s) dominant IMF H-Bonding 2.) covalent network covalent bonds 3.) ionic electrostatic forces 4.) metallic sea of e s between lattice of cations 2.) dry ice, C 2 (s) 3.) benzene, C 6 H 6 (s) 4.) organics (general) LDF LDF dipole-dipole, H-bonding, LDF
chem101/3, wi2010 po 20 9 molecular solids... Details of structure of ice chem101/3, wi2010 po 20 10 mol. solids... Macroscopic Properties soft consistency (easily cut) low m.p. ( ~ 100 C... + 200 C) poor conductivity (electric & thermal) chem101/3, wi2010 po 20 11 2.) Covalent Network Solids giant covalent molecule (covalent bonds from one side of the solid to the other) chem101/3, wi2010 po 20 12 covalent network... Example Structures Diamond Examples: C, diamond C, graphite 2, silica Macroscopic Properties hard, Graphite sp 3 hybridized C atoms sp 2 hybridized C atoms high m.p. conductivity, generally poor but some exceptions: graphite, good electric conductor diamond, good thermal conductor sheets layered on top of each other within sheets: strong bonds between sheets: weak bonds layering responsible for lubricating power e s in π bonds responsible for good el. conductivity
chem101/3, wi2010 po 20 13 covalent network... Example Structures chem101/3, wi2010 po 20 14 covalent network... HT Fig. 20.1 Example Structures: Diamond & Graphite lica, 2, not in 2010 very approximate: each has 4 neighbors each has 2 neighbors chem101/3, wi2010 po 20 15 3.) Ionic Solids chem101/3, wi2010 po 20 16 Pet. Fig. 12.48 Structure of ionic solid 3 D grid of cations/anions see Pet. Fig. 12.48 for an example held together by electrostatic ( Coulombic ) forces stability described by lattice energy (LE) LE = k z 1 z 2 d where, k, positive constant z 1, z 2 charges on ions, d = r 1 + r 2, (distance between nuclei) comment: if LE has lge neg. value, solid is stable
chem101/3, wi2010 po 20 17 ionic solids... absolute value of LE, i.e., LE, if charge, & if size small, highly charged ions make more stable ionic solids Ex. Compare NaCl & Mg Na + Cl Mg 2+ 2 higher charges Mg 2+ smaller than Na + (72pm) (99pm) 2 smaller than Cl (140 pm) (181pm) chem101/3, wi2010 po 20 18 ionic solids... Properties hard & brittle (shatter on impact) high m.p. high, due to high LE electric conductivity : low as solid, but high if molten, or if dissolved in polar solvents, such as H 2 Mg more stable than NaCl; has much higher m.p., useful as lining for fireplaces, furnaces... chem101/3, wi2010 po 20 19 network of cations, 4.) Metallic Solids held together by free (valence ) e s structure not rigid; sea of e s can adjust if cation grid is stressed cation grid easily deformed w/t rupture ( = material is malleable & ductile) chem101/3, wi2010 po 20 20 Metallic Bonding by M Theory can ignore pages 20.20 20.27 in 2010 (Intro. to Band Theory) metal is considered a giant molecule valence A s of all atoms combine to form a densely packed assembly of M s accounts for great bonding strength and good conductivity in metals Properties generally hard (tough to cut) malleable & ductile good conductivity, electrical & thermal
chem101/3, wi2010 po 20 21 Illustration with element #3, Li chem101/3, wi2010 po 20 22 Pet. Fig. 11.34 Metal Bonding by M Theory Li 2 2s A combine σ * σ 2 M's Li 3 3 M's Li n upper half unoccupied lower half occupied conduction band valence band easy transition for e s from valence to conduction band (no energy gap) accounts for mobility of e s = high el. conductivity chem101/3, wi2010 po 20 23 Extension of Band Theory (see Pet Fig. 11.35 & 11.36) ther metals works nicely for group 1 (alkali) metals for group 2 (and other) metals must include involvement of 2p A s to form valence/conduction bands Insulators energy gap between valence & conductance band is too wide no e s can jump across & there is no el. conductivity chem101/3, wi2010 po 20 24 band theory... Semiconductors (, Ge, As...) conductance & valence bands are separated by a small energy gap; thermal energy can promote e s to the conductance band thereby increasing conductivity Effect of Dopants n-type semiconductors typically produced by doping group 14 w/ group 15 elements(e.g., w/ P) produces extra e s which are accommodated in a donor level energy gap between donor level and conductance band is small and material becomes more conducting
chem101/3, wi2010 po 20 25 band theory... chem101/3, wi2010 po 20 26 Pet. Fig. 11.35 Band Theory p-type semiconductors typically produced by doping group 14 w/ group 13 elements (e.g., w/ Al) acceptor level is created for e s of the dopant this level can accept e s from the valence band now we have holes in the valence band and e s can jump from hole to hole to hole, thereby increasing el. conductivity chem101/3, wi2010 po 20 27 Pet. Fig. 11.36 n-type & p-type semiconductors