1 Liquids Liquids Molecules at interfaces behave differently than those in the Molecules at interfaces behave differently than those in the interior. interior. Molecules at surface experience a Molecules at surface experience a net INWARD force of attraction. net INWARD force of attraction. This leads to This leads to SURFACE TENSION SURFACE TENSION — the — the energy req’d to break through the energy req’d to break through the surface. surface.
30
Embed
1 Liquids Molecules at interfaces behave differently than those in the interior. Molecules at surface experience a net INWARD force of attraction. This.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
LiquidsLiquidsMolecules at interfaces behave differently than those in the interior.Molecules at interfaces behave differently than those in the interior.
Molecules at surface experience a net INWARD Molecules at surface experience a net INWARD force of attraction. force of attraction. This leads to This leads to SURFACE TENSIONSURFACE TENSION — the energy — the energy req’d to break through the surface.req’d to break through the surface.
2
Surface TensionSurface Tension
SURFACE TENSIONSURFACE TENSION also leads to spherical liquid also leads to spherical liquid droplets (shape of minimum surface).droplets (shape of minimum surface).
SURFACE TENSIONSURFACE TENSION also leads to spherical liquid also leads to spherical liquid droplets (shape of minimum surface).droplets (shape of minimum surface).
3
LiquidsLiquidsIntermolec. forces also lead to Intermolec. forces also lead to CAPILLARYCAPILLARY
ACTIONACTION and to the existence of a concave and to the existence of a concave meniscus for a water column in a glass tube.meniscus for a water column in a glass tube.
concavemeniscus
H2O in
glasstube
ADHESIVE FORCESbetween water and glass (with polar Si-O bonds)
COHESIVE FORCESbetween watermolecules
4
Capillary ActionCapillary Action
Movement of water up a piece of paper Movement of water up a piece of paper depends on H-bonds between Hdepends on H-bonds between H22O and O and the OH groups of the cellulose in the the OH groups of the cellulose in the paper.paper.
Cohesive forces against the force of gravityCohesive forces against the force of gravity
Problem : Search for applications of capillary action in nature (plants) and in the lab (chromatography)
5
LiquidsLiquidsHigh surface tension due to cohesive forces High surface tension due to cohesive forces
stronger than adhesive forces with the glass stronger than adhesive forces with the glass leads to the existence of a leads to the existence of a convex meniscusconvex meniscus for a column of mercury in a glass tube.for a column of mercury in a glass tube.
convexmeniscus
ADHESIVE FORCESbetween Hg and glass (with polar Si-O bonds)
COHESIVE FORCESNon-polar mercury
Hg in a glass
6
ViscosityViscosityVISCOSITY is the tendency or resistance of liquids to flow.
VISCOSITY is the tendency or resistance of liquids to flow.
Ethanol Glycerol
The resistance to flow results from several factors, includingintermolecular interactions, molecular shape and size.
Do you expect the viscosity of glycerol to be larger or smaller than the viscosity of ethanol ?
7Metallic and Ionic Metallic and Ionic SolidsSolids
Sections 13.6-8Sections 13.6-8
Metallic and Ionic Metallic and Ionic SolidsSolids
Sections 13.6-8Sections 13.6-8Solid-state chemistry is one of the booming areas of science, leading to the development of interesting new materials.
8Types of SolidsTypes of SolidsTable 13.6Table 13.6
5.5. No translations (only No translations (only vibrations, or rotations on vibrations, or rotations on lattice sites) lattice sites)
ZnS, zinc sulfideZnS, zinc sulfide
12
Crystal LatticesCrystal Lattices• Regular 3-D arrangements of equivalent Regular 3-D arrangements of equivalent
LATTICE POINTS in space.LATTICE POINTS in space.• Lattice points define Lattice points define UNIT CELLSUNIT CELLS
– smallest repeating internal unit that has the symmetry smallest repeating internal unit that has the symmetry characteristic of the solid. characteristic of the solid.
13
Cubic Unit CellsCubic Unit Cells
All anglesare 90 degrees
All sidesequal length
There are 7 basic crystal systems, but we are There are 7 basic crystal systems, but we are
only concerned withonly concerned with CUBICCUBIC..
14Cubic Unit Cells of Cubic Unit Cells of MetalsMetalsFigure 13.24Figure 13.24
16Atom Packing in Unit Atom Packing in Unit CellsCells
Assume atoms are hard spheres and that crystals are built Assume atoms are hard spheres and that crystals are built by by PACKINGPACKING of these spheres as efficiently as possible. of these spheres as efficiently as possible.
17Number of Atoms per Unit Number of Atoms per Unit CellCell
Unit Cell Type Unit Cell Type Net Number AtomsNet Number Atoms SC SC BCCBCC FCCFCC
112244
18
Atom Sharing Atom Sharing at Cube Faces and Cornersat Cube Faces and Corners
Atom shared in corner --> 1/8 inside each unit cell
Atom shared in face --> 1/2 inside each unit cell
19
Simple Ionic CompoundsSimple Ionic Compounds
CsCl has a SC lattice of CsCl has a SC lattice of CsCs++ ions with Cl ions with Cl-- in the in the center.center.
1 unit cell has 1 Cl1 unit cell has 1 Cl-- ion ion plus plus
(8 corners)(1/8 Cs(8 corners)(1/8 Cs++ per per corner)corner)
= 1 net Cs= 1 net Cs++ ion. ion.
20
Simple Ionic Simple Ionic CompoundsCompounds
Salts with formula Salts with formula MX can have SC MX can have SC structure — but structure — but not salts with not salts with formula MXformula MX22 or M or M22XX
21
Two Views of CsCl Unit Two Views of CsCl Unit CellCell
Either arrangement leads to formula of 1 Cs+ and 1 Cl- per unit cell
22
NaCl ConstructionNaCl Construction
FCC lattice of Cl- with Na+ in holes
NaNa++ in in octahedral octahedral holesholes
23
Many common salts have FCC arrangements Many common salts have FCC arrangements of anions with cations in of anions with cations in OCTAHEDRAL OCTAHEDRAL HOLESHOLES — e.g., salts such as CA = NaCl — e.g., salts such as CA = NaCl
•• FCC lattice of anions ----> 4 AFCC lattice of anions ----> 4 A--/unit cell/unit cell
•• CC++ in octahedral holes ---> 1 C in octahedral holes ---> 1 C++ at center at center
+ [12 edges • 1/4 C+ [12 edges • 1/4 C++ per edge] per edge]
= 4 C= 4 C++ per unit cell per unit cell
The Sodium Chloride The Sodium Chloride LatticeLattice
24
Comparing NaCl and Comparing NaCl and CsClCsCl
• Even though their formulas have one cation and one anion, the lattices of CsCl and NaCl are different.
• The different lattices arise from the fact that a Cs+ ion is much larger than a Na+ ion.
25Phase DiagramsPhase Diagrams
Lines connect all conditions of T and P where EQUILIBRIUM Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side of the line.exists between the phases on either side of the line.
26
Phase Equilibria — WaterPhase Equilibria — Water
Solid-liquidSolid-liquidGas-LiquidGas-Liquid
Gas-SolidGas-Solid
27
Phases Phases Diagrams—Diagrams—
Important Points Important Points for Waterfor Water
T(˚C)T(˚C) P(mmHg)P(mmHg)
Normal boil point Normal boil point 100100 760760
Normal freeze pointNormal freeze point 00 760760
Triple point Triple point 0.00980.0098 4.58 4.58
28
Solid-Liquid EquilibriaSolid-Liquid EquilibriaIn any system, if you increase P the In any system, if you increase P the DENSITYDENSITY
will go up. will go up.
Therefore — as P goes up, equilibrium favors Therefore — as P goes up, equilibrium favors phase with the larger density (or phase with the larger density (or SMALLERSMALLER volume/gram).volume/gram).