Chapter 10. Liquids and Solids

Transcription

1 Chapter 10. Liquids and Solids Three States of Matter H 2 O Volume constant constant no Shape constant no no Why in three different states? 1

2 Intermolecular Force dipole-dipole attraction V dip-dip : 1. ~ 1% of covalent bond or ionic bond 2. 1/r 2 gas Intermolecular Force dipole-dipole attraction Hydrogen bonding H X:X=N X N, O, F Δχ is big. short H-X distance strong dipole-dipole attraction 2

3 London dispersion force Intermolecular Force V London : 1. Importance for nonpolar molecules 2. 1/r Intermolecular Force London dispersion force < dipole-dipole attraction < Hydrogen bonding 3

4 Intermolecular Force Life much depends on Hydrogen Bonding Ice DNA Protein Properties of Liquid high in energy low in energy tends to reduce surface area surface tension : resistance of a liquid to an increase in its surface area 4

5 capillary action Properties of Liquid cohesive force cohesive force adhesive force adhesive force surface tension Hg H 2 O Solid Structure Powder microcrystals 고체비정형고체 (Amorphous solid) 결정형고체 (Crystalline solid) All solids (crystalline solids) in the universe have a certain number of ways of packing. 5

6 Solids in the Universe 7 Crystal Classes 14 Bravais Lattices 230 Space Groups %%% Spheres: Lattice points Not atoms Solid Structure unit cell lattice point Face-Centered Body-Centered β c a γ α b Solid Structure Crystalline solids Ionic solids Molecular solids Atomic solids Metallic solids Network solids Group 8A solids Ion, molecule, atom 6

7 Structure and Bonding in Metals Metallic Bond Na: 1s 2 2s 2 2p 6 3s 1 Forming sea of electrons (freely-moving valence electrons) Na + Na + Na + Na + Na + Na + e ē ē- Structure? e e - e - Close Packing of Spheres Structure and Bonding in Metals 1926 Goldschmidt proposed atoms could be considered as packing in solids as hard spheres. 7

8 Structure and Bonding in Metals Close Packing of Spheres What is the most effective way of packing spheres in terms of space saving? 1st layer 2nd layer 3rd layer Structure and Bonding in Metals Close Packing of Spheres ABABAB ABCABCABC ABABCBCAB Polytypism Though 2-dimensional structure is the same, 3-dimensional structure is different. Polytypes 8

9 Structure and Bonding in Metals Close Packing of Spheres ABABAB hexagonal closest packing (hcp) Structure and Bonding in Metals Close Packing of Spheres ABCABCABC cubic closest packing (ccp) [face centered cubic (fcc)] 9

10 Solid Structure Solids in the Universe 7 Crystal Classes 14 Bravais Lattices 230 Space Groups %%% Spheres: Lattice points Not atoms Face-Centered Body-Centered All solids (crystalline solids) in the universe have a certain number of ways of packing. β c a γ α b The way of packing Minimizing energy Packing efficiency X-ray Analysis of Solids Solid Structure X-ray yes signal nλ = no signal 경로차 = nλ (n=1,2..) nλ=2dsinθ Bragg's equation 10

11 Solid Structure X-ray Analysis of Solids Structures in Metals Structure and Bonding in Metals Hexagonal-Close Packing (HCP) Cubic-Close Packing (CCP, FCC) Body-Centered Cubic (BCC) Primitive Cubic Diamond Coordination Number: 12 Packing Ratio: 0.74 Hole Size: 0.414r(O h ),225r(T d ) At RT, 1 atm Be, Cd, Co, Mg, Ti, Zn r(O h ) 0.225r(T d ) Ag, AL, Au, Ca, Cu, Ni, Pb, Pt Think about what kinds of hole can exist and sizes. Ba, Cr, Fe, W, alkai metals Po Si, Ge, Sn, Pb 11

12 Ex) How many spheres in a closest packing structures? ccp Structure and Bonding in Metals Close Packing of Spheres 1 1 net number of spheres in the unit cell = = Ex) Ag: ccp, r= 144pm. What is the density of the solid Ag (atomic mass=107.9)? d 4r d 2 d = + d 2 2 = (4r), d = r mass volume 8 = 144 pm (4)(107.9g / = 12 3 ( m) = g /(100cm) = 10.6g / cm 8 = m ) 7 3 = g / m Structure and Bonding in Metals Bonding molels in metals Na: 1s 2 2s 2 2p 6 3s 1 Forming sea of electrons (freely-moving valence electrons) Na + Na + Na + e ē ē- e ē - Na + Na + properties of metals : malleability, ductilty, conduction of heat and electricity (omnidirectional) How to explain? 12

13 Structure and Bonding in Metals Bonding molels in metals Molecular orbital model (band model) atomic orbital molecular orbitals... : : :... : Metal Alloys Structure and Bonding in Metals substitutional alloy interstitial alloy 13

14 Network Atomic Solids Composed of strong directional covalent bonds that are best viewed as a giant molecule" Carbon-based compounds do not conduct heat or electricity carbon, silicon-based typical metal sp 3 sp 2 Network Atomic Solids Silicon-based compounds Silica (emprical formula:sio 2 ) CO 2 (gas) O=C=O SiO 2 (gas?) O=Si=O σ bond: sp(c)+ sp 2 (O) π bond: 2p(C) + 2p(O) not effective σ bond: sp(si)+ sp 2 (O) π bond: 3p(Si) + 2p(O) SiO 2 forming > 1600 o C Cooling σ bond: sp 3 (Si)+ sp 3 (O) glass quartz 14

15 Network Atomic Solids Silicon-based compounds Silicate (emprical formula:si n O m k- ) Silicon-based compounds Network Atomic Solids Si Semiconductors large (insulator) not large, when T up, conductivity up (semiconductor) Si Diamond (C) metal (when T up, conductivity down) 15

16 Silicon-based compounds Network Atomic Solids Si Semiconductors yes current --> no current no current p-n junction yes current amplifier Molecular Solids Ice (H 2 O) Dry ice (CO 2 ) Sulfur crystal (S 8 ) white phosphorus (P 4 ) hydrogen bonding London dispersion force 16

17 Holes in closest packing Ionic Solids Ionic compounds Cl - (FCC) Na + (O h hl) hole) NaCl S 2- (FCC) ZnS Zn 2+ (half of T d hole) Ionic Solids Ionic compounds How many Cl - s in NaCl unit cell? How many Na + s (O h holes) in NaCl unit cell? Cl - (FCC) Na + (O h hl) hole) How many S 2- s in ZnS unit cell? How many T d holes in ZnS unit cell? NaCl S 2- (FCC) ZnS Zn 2+ (half of T d hole) 17

18 Vapor Pressure and Changes of State evaporation condensation Vapor Pressure and Changes of State vapor pressure : the pressure of the vapor present at equilibrium. 18

19 Vapor Pressure and Changes of State measuring vapor pressure add liquid vapor pressure < < intermolecular force > > Vapor Pressure and Changes of State why evaporate? T 1 < T 2 P vap (T 1 ) < P vap (T 2 ) 19

20 Vapor Pressure and Changes of State vapor pressure ΔH vap : heat of vaporization ΔH vap ln(p vap ) = - ( 1 R T ) + C y = mx + b Vapor Pressure and Changes of State changes of state boiling point need heat of vaporization melting point need heat of fusion heating curve (at 1 atm) 20

21 Vapor Pressure and Changes of State changes of state melting point: Molecules break loose from lattice points and solid changes to liquid. (Temperature is constant as melting occurs.) vapor pressure of solid = vapor pressure of liquid case 1: vapor pressure of solid > vapor pressure of liquid (>0 o C) * solid --> vapor --> liquid * at equilibrium: liquid and vapor case 2: vapor pressure of solid < vapor pressure of liquid (<0 o C) * liquid --> vapor --> solid * at equilibrium: solid and vapor case 3: vapor pressure of solid = vapor pressure of liquid (=0 o C) * at equilibrium: solid and liquid (melting point) (and vapor) Vapor Pressure and Changes of State changes of state boiling point: Constant temperature when added energy is used to vaporize the liquid. vapor pressure of liquid = pressure of surrounding atmosphere Water in a closed system with a pressure of 1 atm exerted on the piston. No bubbles can form within the liquid as long as the vapor pressure is less than 1 atm. Supercooling Superheating 21

22 Phase Diagram Represents phases as a function of temperature and pressure in a closed system. critical point: critical temperature and pressure (for water, T c = 374 C and 218 atm). critical ii temperature: temperature above which the vapor can not be liquefied. critical pressure: pressure required to liquefy AT the critical temperature. vapor pressure of liquid, also boiling temperature variation depending on the external pressure H 2 O melting temperature variation depending on the external pressure vapor pressure of solid, also boiling temperature variation depending on the external pressure Phase Diagram Experiments Piston pressure at start (-20 o C) Ice Piston pressure 225 atm 1 atm 4.8 torr 2.0 torr 22

23 Phase Diagram Phase Diagram Surface Melting 23

24 Phase Diagram CO 2 24