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Liquids. Molecules at interfaces behave differently than those in the interior. Molecules at surface experience a net INWARD force of attraction. This leads to SURFACE TENSION — the energy req’d to break through the surface. Surface Tension.

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liquids
Liquids

Molecules at interfaces behave differently than those in the interior.

Molecules at surface experience a net INWARD force of attraction.

This leads to SURFACE TENSION — the energy req’d to break through the surface.

surface tension
Surface Tension

SURFACE TENSION also leads to spherical liquid droplets (shape of minimum surface).

liquids1

concave

ADHESIVE FORCES

meniscus

between water and glass

(with polar Si-O bonds)

H

O in

2

COHESIVE FORCES

glass

between water

tube

molecules

Liquids

Intermolec. forces also lead to CAPILLARYACTION and to the existence of a concave meniscus for a water column in a glass tube.

capillary action
Capillary Action

Cohesive forces against the force of gravity

Movement of water up a piece of paper depends on H-bonds between H2O and the OH groups of the cellulose in the paper.

Problem : Search for applications of capillary action

in nature (plants) and in the lab (chromatography)

liquids2

convex

ADHESIVE FORCES

meniscus

between Hg and glass

(with polar Si-O bonds)

COHESIVE FORCES

Non-polar mercury

Liquids

High surface tension due to cohesive forces stronger than adhesive forces with the glass leads to the existence of a convex meniscus for a column of mercury in a glass tube.

Hg in a glass

viscosity
Viscosity

VISCOSITYis the tendency or resistance of liquids to flow.

Do you expect the viscosity of glycerol to be larger or

smaller than the viscosity of ethanol ?

Ethanol

Glycerol

The resistance to flow results from several factors, including

intermolecular interactions, molecular shape and size.

metallic and ionic solids sections 13 6 8
Metallic and Ionic SolidsSections 13.6-8

Solid-state chemistry is one of the booming areas of science, leading

to the development of interesting new materials.

types of solids table 13 6
Types of SolidsTable 13.6

TYPE Composition BINDING FORCES

Ionic NaCl, CaF2, ZnS Ion-ion

Metallic Na, Fe Metallic

Molecular Ice, I2 Dipole Ind. dipole

Network Diamond Extended Graphite covalent

Amorphous

Glass, polyethylene

Covalently bonded

Networks with no

Long-range

Regularity.

network solids
Network Solids

Diamond

Graphite

network solids1
Network Solids

A comparison of diamond (pure carbon) with silicon.

properties of solids
Properties of Solids

1. Molecules, atoms or ions locked into a CRYSTAL LATTICE

2. Particles are CLOSE together

3. STRONG IM forces

  • Highly ordered, rigid, incompressible
  • No translations (only vibrations, or rotations on lattice sites)

ZnS, zinc sulfide

crystal lattices
Crystal Lattices
  • Regular 3-D arrangements of equivalent LATTICE POINTS in space.
  • Lattice points define UNIT CELLS
    • smallest repeating internal unit that has the symmetry characteristic of the solid.
cubic unit cells

All sides

equal length

All angles

are 90 degrees

Cubic Unit Cells

There are 7 basic crystal systems, but we are only concerned withCUBIC.

cubic unit cells of metals figure 13 24
Cubic Unit Cells of MetalsFigure 13.24

Simple cubic (SC)

Body-centered cubic (BCC)

Face-centered cubic (FCC)

1 atom/unit cell

2 atoms/unit cell

4 atoms/unit cell

atom packing in unit cells
Atom Packing in Unit Cells

Assume atoms are hard spheres and that crystals are built by PACKING of these spheres as efficiently as possible.

number of atoms per unit cell
Number of Atoms per Unit Cell

1

Unit Cell Type Net Number Atoms

SC

BCC

FCC

2

4

atom sharing at cube faces and corners
Atom Sharing at Cube Faces and Corners

Atom shared in corner

--> 1/8 inside each unit cell

Atom shared in face

--> 1/2 inside each unit cell

simple ionic compounds
Simple Ionic Compounds

CsCl has a SC lattice of Cs+ ions with Cl- in the center.

1 unit cell has 1 Cl- ion plus

(8 corners)(1/8 Cs+ per corner)

= 1 net Cs+ ion.

simple ionic compounds1
Simple Ionic Compounds

Salts with formula MX can have SC structure — but not salts with formula MX2 or M2X

two views of cscl unit cell
Two Views of CsCl Unit Cell

Either arrangement leads to formula of 1 Cs+ and 1 Cl- per unit cell

nacl construction

Na+ in octahedral holes

NaCl Construction

FCC lattice of Cl- with Na+ in holes

the sodium chloride lattice
The Sodium Chloride Lattice

Many common salts have FCC arrangements of anions with cations in OCTAHEDRAL HOLES — e.g., salts such as CA = NaCl

• FCC lattice of anions ----> 4 A-/unit cell

• C+ in octahedral holes ---> 1 C+ at center

+ [12 edges • 1/4 C+ per edge]

= 4 C+ per unit cell

comparing nacl and cscl
Comparing NaCl and CsCl
  • 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.
phase diagrams
Phase Diagrams

Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side of the line.

phase equilibria water
Phase Equilibria — Water

Gas-Liquid

Solid-liquid

Gas-Solid

phases diagrams important points for water
Phases Diagrams—Important Points for Water

T(˚C) P(mmHg)

Normal boil point 100 760

Normal freeze point 0 760

Triple point 0.0098 4.58

solid liquid equilibria
Solid-Liquid Equilibria

In any system, if you increase P the DENSITYwill go up.

Therefore — as P goes up, equilibrium favors phase with the larger density (or SMALLERvolume/gram).

Liquid H2OSolid H2O

Density 1 g/cm3 0.917 g/cm3

cm3/gram 1 1.09

solid liquid equilibria1
Solid-Liquid Equilibria

Raising the pressure at constant T causes water to melt.

The NEGATIVE SLOPE of the S/L line is unique to H2O. Almost everything else has positive slope.

solid vapor equilibria
Solid-Vapor Equilibria

At P < 4.58 mmHg and T < 0.0098 ˚C

solid H2O can go directly to vapor. This process is called SUBLIMATION

This is how a frost-free refrigerator works.