Dr. S. M. Condren Chapter 15 The Liquid State, The Solid State, and Modern Materials.

Dr. S. M. Condren

Chapter 15

The Liquid State, The Solid State, and Modern Materials

Dr. S. M. Condren

Properties of Liquids

surface tension - A property of liquids arising from unbalanced molecular cohesive forces at or near the surface

Dr. S. M. Condren

Properties of Liquids

surface tension

capillary action - phenomenon in which the surface of a liquid is elevated or depressed when it comes in contact with a solid

Dr. S. M. Condren

Properties of Liquidssurface tension

capillary action

viscosity

– resistance of a fluid to flow

– resistance acts against the motion of any solid object through the fluid, and also against motion of the fluid itself past stationary obstacles

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Compared to the average energy, those molecules which escape the surface of a liquid are

lower in energy

same energy

higher in energy

Dr. S. M. Condren

Phase Changes

Evaporation

phase change from liquid to gas

Condensation

phase change from gas to liquid

Dr. S. M. Condren

Vapor Pressure vs. Temperature

p vs. t(oC)

exponential function as t increases, p increases

Dr. S. M. Condren

Dr. S. M. Condren

Pressure vs. Temperature

0

200

400

600

800

1000

1200

0 20 40 60 80 100 120

Temperature, C

Va

po

r P

ress

ure

, to

rr

Dr. S. M. Condren

ln P vs 1/T

0.5

1

1.5

2

2.5

3

0.0025 0.0027 0.0029 0.0031 0.0033 0.0035 0.0037 0.0039

1/T, 1/K

ln P

Dr. S. M. Condren

Vapor Pressure vs. Temperature

Clausius-Clapeyron Equation

ln(P2/P1)=(Hvap/R)(1/T1 - 1/T2)

Dr. S. M. Condren

Properties of Liquidsboiling point

• the temperature at which its vapor pressure is equal to the local atmospheric pressure

normal boiling point

• the temperature at which its vapor pressure is equal to one atmospheric pressure

Dr. S. M. Condren

Properties of Liquids

liquid-vapor equilibirum

• both liquid and vapor of the liquid present in the same container uder stable conditions

vapor pressure

• The pressure exerted by a vapor in equilibrium with its solid or liquid phase.

Dr. S. M. Condren

Properties of Liquids

enthalpy of vaporization - The amount of heat required to convert a unit mass of a liquid at its boiling point into vapor without an increase in temperature.

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Phase Changes

Melting

phase change from solid to liquid

Freezing

phase change from liquid to solid

melting point(freezing point)

temperature at which a liquid congeals into the solid state at a given pressure

Dr. S. M. Condren

Dr. S. M. Condren

Phase Changes

Melting and Freezing

enthalpy of fusion - heat absorbed by the substance in changing its state without raising its temperature

Dr. S. M. Condren

Dr. S. M. Condren

Phase ChangesLiquid Crystals

• substance that behaves like both a liquid and a solid

• by applying a small electric field, certain liquid crystal substances gain the ability to rotate polarized light. These types of liquid crystals are used to construct displays used in digital watches, calculators, miniature television sets, portable computers, and other items

Dr. S. M. Condren

Dr. S. M. Condren

Phase Diagram - General

P

T

Solid

Gas

Liquid

1 atm mpnbp

triple point

critical point

x sublimation point

x x

Dr. S. M. Condren

Phase Diagrams

label axes

label phase regions

label: triple point

critical point

melting point

boiling point

sublimation point

Dr. S. M. Condren

Critical Point

• The temperature and pressure at which the liquid and gaseous phases of a pure stable substance become identical.

• The critical temperature of a gas is the maximum temperature at which the gas can be liquefied; the critical pressure is the pressure necessary to liquefy the gas at the critical temperature.

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Solids

• Crystals

• X-ray Diffraction

• Bragg's Law

Dr. S. M. Condren

Solids

Crystals - A homogenous solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between constituent parts.

Dr. S. M. Condren

SolidsX-ray Diffraction - When an X-ray beam

bombards a crystal, the atomic structure of the crystal causes the beam to scatter in a specific pattern. This phenomenon, known as X-ray diffraction, occurs when the wavelength of the X rays and the distances between atoms in the crystal are of similar magnitude.

Dr. S. M. Condren

Solids

Bragg's Law - The fundamental law of x-ray crystallography, n = 2dsin, where n is an integer, is the wavelength of a beam of x-rays incident on a crystal with lattice planes separated by distance d, and is the Bragg angle.

[After Sir William Henry Bragg and Sir William Lawrence Bragg.]

Dr. S. M. Condren

Structure Determination

High Voltage

X-Ray DiffractionX-ray Tube

Lead Screen

X-ray Beam

Crystal

Photographic Plate

Projection Screen

Visible Light Laser 35mm slide

Optical Transforms

L

X

Dr. S. M. Condren

Diffraction Conditions

Solid State Resources CD-ROM

Movies

Chapter 4

Dr. S. M. Condren

Diffraction ConditionsFraunhofer diffraction Bragg diffraction

For constructive interference, d sin = n

For constructive interference, 2(d sin ) = n

}d

d }}

d

d sin

}

}d

d sin d sin

Dr. S. M. Condren

Solids

Bragg's Law

n = 2d sinwhere n => order of diffraction

=> X-ray wavelength

d => spacing between layers

of atom

=> angle of diffraction

Dr. S. M. Condren

EXAMPLE

What is the spacing between copper atoms if X-ray radiation of wavelength 1.54diffracts in the second order at 58.42°?

n = 2 = 1.54A = 58.42° d = ?

n = 2d sin

d = (n)/2sin = (2*1.54A)/(2*sin(58.42°))

= 1.54A/0.852 = 1.81

Dr. S. M. Condren

Dr. S. M. Condren

Ionic Solids

cations and anions form the points in the 3-D structure

• NaCl

Dr. S. M. Condren

Metallic Solids

atoms of the metal form the 3-D points in the structure

• iron

• copper

Dr. S. M. Condren

Molecular Solids

molecules form point in the 3-D structure

• sugar

Dr. S. M. Condren

Network Covalent Solids

atoms covalently bonded to the surrounding atoms in a 3-D network

• diamond

• quartz

Dr. S. M. Condren

Lattice and Units Cells

Lattices

7 types

4 most common types: cubic

orthorhombic

monoclinic

triclinic

Dr. S. M. Condren

Unit Cells?

Dr. S. M. Condren

Which are Unit Cells?

Dr. S. M. Condren

Unit Cells of Metals

cubic: a = b = c

= = = 90°

simple cubic (primitive cubic) atoms only at corners of cube

body centered cubic (BCC) atoms at the corners and at the center of the body.

face-centered cubic (FCC) atoms at the corners and at the center of all 6 faces, same as cubic close-packed.

Dr. S. M. Condren

Dr. S. M. Condren

Structures of Metallic Elements

Ru

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

Hf

V

Nb

Ta

Cr

Mo

W

Mn

Tc

Re

Fe

Os

Co

Ir

Rh

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

B

Al

Ga

In

Tl

C

Si

Ge

Sn

Pb

N

P

As

Sb

Bi

O

S

Se

Te

Po

F

Cl

Br

I

At

Ne

Ar

Kr

Xe

Rn

He

Primitive Cubic

Body Centered Cubic

Cubic close packing(Face centered cubic)

Hexagonal close packing

Dr. S. M. Condren

Number of Atoms per Unit Cell

- atoms at corner of unit cell count 1/8

- atoms at center of a face count 1/2

- atoms at center of the body count 1

Dr. S. M. Condren

Dr. S. M. Condren

Primitive Cubic

use of an orange to show why only 1/8 atom at corners of a unit cell

Solid State Resources CD-ROM

Chapter 3

Movie Orange Slicing

Dr. S. M. Condren

Number of Atoms per Unit Cell

primitive cubic => 8(1/8) = 1

BCC => 8(1/8) + 1 = 2

FCC => 8(1/8) + 6(1/2) = 4

Dr. S. M. Condren

Combinations of ElementsElement Combination Likely Structure

Nonmetal and nonmetal Discrete moleculeCO2, PCl3, NO

Metal and metal Extended (alloys)CuZn (brass), NiTi

Metal and nonmetal Extended (salts)NaCl, ZnS, CaTiO3

Dr. S. M. Condren

Unit Cells of Compounds

cubic: a = b = c

= = = 90°

face-centered cubic (FCC) =>NaCl, LiCl, ZnS(zinc blend, S ions in FCC with Zn ions in tetrahedral holes)

Dr. S. M. Condren

Dr. S. M. Condren

NaCl Stoichiometry

8 corners X 18 12 edges X

14

6 faces X 12 1 center X 1

---------------- ----------------4 Cl- ions 4 Na+ ions

z=0, 1 z=1/2

NaCl has 1:1 stoichiometry!

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Why is CsCl not

body-centered cubic (BCC)?

Dr. S. M. Condren

Unit Cells of Compounds

orthorhombic: abc

= = = 90°

monoclinic: a b c

= = 90°

> 90°

triclinic: ab c

90°

Dr. S. M. Condren

EXAMPLE

Metallic gold crystallizes in the face-centered cubic lattice. The length of the cubic unit cell is 4.070A. What is the closest distance between gold atoms?

a = 4.070 r = ? closest distance = 2r

Dr. S. M. Condren

Face-Centered-Cubic Unit Cell

df = face diagonal

r = radius of atom

df = 4r

a = edge

a2 + a2 = df2

2a2 = (4r)2

r = (a*21/2 )/4

Dr. S. M. Condren

EXAMPLEMetallic gold crystallizes in the face-centered cubic lattice. The length of the cubic unit cell is 4.070A. What is the closest distance between gold atoms?

a = 4.070A r = ? closest distance = 2r

4r = a21/2 => r = a21/2/4

r = (4.070A*1.414)/4 = 1.44A

closest distance = 2(1.44A) = 2.88A

Dr. S. M. Condren

Molecular Substances

Common Properties

- nonconductors of electricity when pure

- insoluble in water but soluble in non-polar solvents

- volatile, appreciable vapor pressure at room temperature

- low melting and boiling points

Dr. S. M. Condren

Metals

Common Properties

– Nonvolatile.

– Insoluble in water and other common solvents.

Dr. S. M. Condren

Dr. S. M. Condren

Network Covalent Substances

graphite => sp2 hybrid C, planar

Dr. S. M. Condren

Dr. S. M. Condren

Network Covalent Substances

diamond => sp3 hybrid C, 3D

Dr. S. M. Condren

Dr. S. M. Condren

Network Covalent Substances

silicon dioxide => sp3 Si, 4 O around each

Si

=> sp3 O, 4 Si around each

Si

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Dr. S. M. Condren

Amorphous Solids (Glasses)

• lacking definite form

• no long range ordering in the structure