ch-2 compatibility mode

7/28/2019 Ch-2 Compatibility Mode

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ATOMIC BONDING INSOLIDS


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ISSUES TO ADDRESS...ISSUES TO ADDRESS...ISSUES TO ADDRESS...ISSUES TO ADDRESS...

What promotes bonding?

BONDING AND PROPERTIES

What types of bonds are there?

What properties are inferred from bonding?


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orbital electrons:n = principalquantum number

n=3 21

BOHR ATOM

Nucleus: Z = # protons

= 1 for hydrogen to 94 for plutoniumN = # neutrons

Atomic mass A Z + N


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have discrete energy states tend to occupy lowest available energy state.

ergy

n=44p

3d

Electrons...ELECTRON ENERGY STATES

Inc

reasinge

n=1

n=2

n=3

1s

2s

3s

2p

3ps


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have complete s and p subshells tend to be unreactive.

Stable electron configurations...

Z Element Configuration

STABLE ELECTRON

CONFIGURATIONS

10 Ne 1s22s22p6

18 Ar 1s22s22p63s23p6

36 Kr 1s22s22p63s23p63d104s24p6


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Most elements: Electron configuration not stable.ElementHydrogen

Helium

LithiumBerylliumBoronCarbon

Atomic #1

2

3456

Electron configuration1s1

1s2 (stable)

1s22s11s22s21s22s22p11s22s22p2

SURVEY OF ELEMENTS

Why? Valence (outer) shell usually not filled completely.

...

NeonSodiumMagnesiumAluminum...

Argon...Krypton

10111213

18...36

...

1s22s22p6 (stable)1s22s22p63s11s22s22p63s21s22s22p63s23p1...

1s22s22p63s23p6 (stable)...

1s22s22p63s23p63d104s246 (stable)


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Columns: Similar Valence Structure

He

iner

tgases

accept1e

accept2e

give

up1e

giveup2e

eup3e

Metal

Nonmetal

Intermediate

H

THE PERIODIC TABLE

Electropositive elements:Readily give up electrons

to become + ions.

Electronegative elements:Readily acquire electrons

to become - ions.

Ar

Kr

Xe

Rn

gi

v

Na Cl

Br

I

At

SMg

Ca

Sr

Ba

Ra

K

Rb

Cs

Fr

Sc

Y

Se

Te

Po


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Ranges from 0.7 to 4.0

He

-

Ne-

Ar-

F4.0

Cl3.0

Li1.0

Na0.9

H

2.1

Be1.5

Mg1.2

Large values: tendency to acquire electrons.

ELECTRONEGATIVITY

Smaller electronegativity Larger electronegativity

-Xe

-

Rn-

2.8I

2.5

At2.2

0.8Rb0.8

Cs0.7

Fr0.7

1.0Sr1.0

Ba0.9

Ra0.9

1.5

1.6

1.8

1.8

1.8

2.0


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Interatomic ForcesInteratomic ForcesInteratomic ForcesInteratomic Forces

Attractive repulsiveAttractive repulsiveAttractive repulsiveAttractive repulsive

Magnitude of eachMagnitude of eachMagnitude of eachMagnitude of eacha fn. ofa fn. ofa fn. ofa fn. of

Net force bet. two atomsNet force bet. two atomsNet force bet. two atomsNet force bet. two atomsFFFFNNNN=F=F=F=FAAAA + F+ F+ F+ FRRRR

When FWhen FWhen FWhen FNNNN and Fand Fand Fand FRRRR balance,balance,balance,balance,FFFFNNNN = 0= 0= 0= 0


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rrrr0000 corresponds tocorresponds tocorresponds tocorresponds toseparation distanceseparation distanceseparation distanceseparation distance

at min. of P.E curve,at min. of P.E curve,at min. of P.E curve,at min. of P.E curve,EEEE0000 and shape of E vs r curveand shape of E vs r curveand shape of E vs r curveand shape of E vs r curve

vary fromvary fromvary fromvary fromMATERIAL TO MATERIALMATERIAL TO MATERIALMATERIAL TO MATERIALMATERIAL TO MATERIAL

and depend on theand depend on theand depend on theand depend on the


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BONDING IN MATERIALS

Primary Bonding Secondary Bonding

(Intra molecular (Intermolecular forces 1 to 40kJ mol-1)150 to 800kJ mol-1 )

(Vanderwaals Bonding)(inert gases)

Ionic Covalent Metallic(NaCl,MgO, (CH4,Ge,C,SiC, (all elemental metals)

a 2 e c. a s, amon

etc.)

Non-directional Directional

(many nonmetallicmolecules)

When a bond is formed the total energy inWhen a bond is formed the total energy inWhen a bond is formed the total energy inWhen a bond is formed the total energy inBONDED STATE is < that in the FREE STATEBONDED STATE is < that in the FREE STATEBONDED STATE is < that in the FREE STATEBONDED STATE is < that in the FREE STATEFor both IONIC and COVALENT BONDINGFor both IONIC and COVALENT BONDINGFor both IONIC and COVALENT BONDINGFor both IONIC and COVALENT BONDING

Association can take place when theAssociation can take place when theAssociation can take place when theAssociation can take place when the

bonded state achieves the stabilitybonded state achieves the stabilitybonded state achieves the stabilitybonded state achieves the stabilityie A STATE OF MINIMUM ENERGYie A STATE OF MINIMUM ENERGYie A STATE OF MINIMUM ENERGYie A STATE OF MINIMUM ENERGY

When two atoms combine,energy must be releasedWhen two atoms combine,energy must be releasedWhen two atoms combine,energy must be releasedWhen two atoms combine,energy must be releasedso that total energy is lowered. This is known asso that total energy is lowered. This is known asso that total energy is lowered. This is known asso that total energy is lowered. This is known as

BONDING ENERGYBONDING ENERGYBONDING ENERGYBONDING ENERGY


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ELECTRONIC CONFIGURATION OF ALLIONS OF A SIMPLE IONIC CRYSTAL

SHOWS CLOSE ELECTRONIC

SHELLSCHARGE DISTRIBUTION IS

SPHERICALLY SYMMETIRC

INERT GASESFOR IONIC CRYSTAL TO BE STABLE,ALL POSITIVE IONS MUST HAVE ASFOR IONIC CRYSTAL TO BE STABLE,ALL POSITIVE IONS MUST HAVE ASFOR IONIC CRYSTAL TO BE STABLE,ALL POSITIVE IONS MUST HAVE ASFOR IONIC CRYSTAL TO BE STABLE,ALL POSITIVE IONS MUST HAVE AS

NEAREST NEIGHBOURS NEGATIVELY CHARGED IONS IN A 3D SCHEME.NEAREST NEIGHBOURS NEGATIVELY CHARGED IONS IN A 3D SCHEME.NEAREST NEIGHBOURS NEGATIVELY CHARGED IONS IN A 3D SCHEME.NEAREST NEIGHBOURS NEGATIVELY CHARGED IONS IN A 3D SCHEME.NON DIRECTIONAL BONDING:NON DIRECTIONAL BONDING:NON DIRECTIONAL BONDING:NON DIRECTIONAL BONDING: MAGNITUDE OF THE BOND IS EQUAL IN ALLMAGNITUDE OF THE BOND IS EQUAL IN ALLMAGNITUDE OF THE BOND IS EQUAL IN ALLMAGNITUDE OF THE BOND IS EQUAL IN ALL

DIRECTIONS AROUND AN ION ( EACH ION HAS A UNIFORMLY DISTRIBUTEDDIRECTIONS AROUND AN ION ( EACH ION HAS A UNIFORMLY DISTRIBUTEDDIRECTIONS AROUND AN ION ( EACH ION HAS A UNIFORMLY DISTRIBUTEDDIRECTIONS AROUND AN ION ( EACH ION HAS A UNIFORMLY DISTRIBUTEDELECTRIC FIELD,ONE CANNOT PREDICT THAT A PARTICULAR ION ISELECTRIC FIELD,ONE CANNOT PREDICT THAT A PARTICULAR ION ISELECTRIC FIELD,ONE CANNOT PREDICT THAT A PARTICULAR ION ISELECTRIC FIELD,ONE CANNOT PREDICT THAT A PARTICULAR ION ISBONDED TO THIS OR THAT ATOM).BONDED TO THIS OR THAT ATOM).BONDED TO THIS OR THAT ATOM).BONDED TO THIS OR THAT ATOM).

PREDOMINANT BONDING IN CERAMIC MATERIALS IS IONICPREDOMINANT BONDING IN CERAMIC MATERIALS IS IONICPREDOMINANT BONDING IN CERAMIC MATERIALS IS IONICPREDOMINANT BONDING IN CERAMIC MATERIALS IS IONIC


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Attractive bonding forces areAttractive bonding forces areAttractive bonding forces areAttractive bonding forces are COULOMBICCOULOMBICCOULOMBICCOULOMBIC (between positive and negative ions)(between positive and negative ions)(between positive and negative ions)(between positive and negative ions)For two isolated ions ,For two isolated ions ,For two isolated ions ,For two isolated ions ,

he attractive energy Ehe attractive energy Ehe attractive energy Ehe attractive energy Eaaaa is a function of theis a function of theis a function of theis a function of the INTERATOMIC DISTANCEINTERATOMIC DISTANCEINTERATOMIC DISTANCEINTERATOMIC DISTANCE according toaccording toaccording toaccording toEEEEaaaa ==== ----A / r , A=(zA / r , A=(zA / r , A=(zA / r , A=(z1111e )(ze )(ze )(ze )(z2222e)/4e)/4e)/4e)/40000,

(MADELUNG Energy) , Similarly for the repulsive energy, E(MADELUNG Energy) , Similarly for the repulsive energy, E(MADELUNG Energy) , Similarly for the repulsive energy, E(MADELUNG Energy) , Similarly for the repulsive energy, E bbbb = B / r= B / r= B / r= B / rnnnn

A,B and n are constants and their values depend on the particular ionic systemA,B and n are constants and their values depend on the particular ionic systemA,B and n are constants and their values depend on the particular ionic systemA,B and n are constants and their values depend on the particular ionic system


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REAL IONIC CRYSTAL:approximately spherical symmetry ,some distortion near the region of

contact with neighbouring atoms


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Na metal Cl nonmetal

Occurs between + and - ions. Requires electron transfer.

Large difference in electronegativity required.

Example: NaCl

IONIC BONDING

unstable unstableelectron

+ -CoulombicAttraction

Na (cation)stable Cl (anion)stable


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Predominant bonding in Ceramics

He-

Ne-

Ar

F4.0

Cl

Li1.0

Na

H2.1

Be1.5

Mg

CsCl

MgO

CaF2

NaCl

O3.5

EXAMPLES: IONIC BONDING

Give up electrons Acquire electrons

-

Kr-

Xe-

Rn-

.

Br2.8

I2.5

At2.2

.

K0.8

Rb0.8

Cs0.7

Fr0.7

.

Ca1.0

Sr1.0

Ba0.9

Ra0.9

Ti1.5

Cr1.6

Fe1.8

Ni1.8

Zn1.8

As2.0

Good conductors of heat and electricity in molten state or aqueous mediumGood conductors of heat and electricity in molten state or aqueous mediumGood conductors of heat and electricity in molten state or aqueous mediumGood conductors of heat and electricity in molten state or aqueous medium


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LATTICELATTICELATTICELATTICE is a regular geometrical array formed by a large no. of +ve andis a regular geometrical array formed by a large no. of +ve andis a regular geometrical array formed by a large no. of +ve andis a regular geometrical array formed by a large no. of +ve and ve ionsve ionsve ionsve ionsheld togetherby elecrostatic attraction.held togetherby elecrostatic attraction.held togetherby elecrostatic attraction.held togetherby elecrostatic attraction.

Energy released during the formation of a lattice is known asEnergy released during the formation of a lattice is known asEnergy released during the formation of a lattice is known asEnergy released during the formation of a lattice is known as LATTICE ENERGYLATTICE ENERGYLATTICE ENERGYLATTICE ENERGY

LatticeLatticeLatticeLattice is a highly stable arrangement. For high lattice energy, size of cation < size of anion,is a highly stable arrangement. For high lattice energy, size of cation < size of anion,is a highly stable arrangement. For high lattice energy, size of cation < size of anion,is a highly stable arrangement. For high lattice energy, size of cation < size of anion,

more effective is the nucleus of the cation to pull the neighbouring anion towardsmore effective is the nucleus of the cation to pull the neighbouring anion towardsmore effective is the nucleus of the cation to pull the neighbouring anion towardsmore effective is the nucleus of the cation to pull the neighbouring anion towards itititit


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Requires shared electrons

Example: CH4

C: has 4 valence e,needs 4 more

H: has 1 valence e,

shared electrons

from carbon atom

H

H

H C

CH4

COVALENT BONDING

needs 1 moreElectronegativitiesare comparable.

shared electronsfrom hydrogenatoms

H


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Covalent Bond ELECTRONS IN COVALENT BOND AREELECTRONS IN COVALENT BOND AREELECTRONS IN COVALENT BOND AREELECTRONS IN COVALENT BOND ARE

LOCALIZED IN THE REGIONS BETWEENLOCALIZED IN THE REGIONS BETWEENLOCALIZED IN THE REGIONS BETWEENLOCALIZED IN THE REGIONS BETWEENTHE TWO ATOMS JOINED BY THE BONDTHE TWO ATOMS JOINED BY THE BONDTHE TWO ATOMS JOINED BY THE BONDTHE TWO ATOMS JOINED BY THE BOND

POSSIBLE NUMBER OF COVALENT BONDSPOSSIBLE NUMBER OF COVALENT BONDSPOSSIBLE NUMBER OF COVALENT BONDSPOSSIBLE NUMBER OF COVALENT BONDS

NO. OF VALENCE ELECTRONS = NNO. OF VALENCE ELECTRONS = NNO. OF VALENCE ELECTRONS = NNO. OF VALENCE ELECTRONS = NNO. OF COVALENT BONDS = 8NO. OF COVALENT BONDS = 8NO. OF COVALENT BONDS = 8NO. OF COVALENT BONDS = 8----N (by octet rule forN (by octet rule forN (by octet rule forN (by octet rule forstability of atoms)stability of atoms)stability of atoms)stability of atoms)

INTER ATOMIC BONDING : PARTIALLY IONIC andINTER ATOMIC BONDING : PARTIALLY IONIC andINTER ATOMIC BONDING : PARTIALLY IONIC andINTER ATOMIC BONDING : PARTIALLY IONIC andPARTIALLY COVALENTPARTIALLY COVALENTPARTIALLY COVALENTPARTIALLY COVALENT

GREATER THE DIFF. IN ELECTRONEGATIVITY MOREGREATER THE DIFF. IN ELECTRONEGATIVITY MOREGREATER THE DIFF. IN ELECTRONEGATIVITY MOREGREATER THE DIFF. IN ELECTRONEGATIVITY MOREIONIC NATURE OF THE BOND (IONIC NATURE OF THE BOND (IONIC NATURE OF THE BOND (IONIC NATURE OF THE BOND (larger the separation bothlarger the separation bothlarger the separation bothlarger the separation both

column wise or row wise in the Periodic Table, more ionic nature ofcolumn wise or row wise in the Periodic Table, more ionic nature ofcolumn wise or row wise in the Periodic Table, more ionic nature ofcolumn wise or row wise in the Periodic Table, more ionic nature ofthe bond)the bond)the bond)the bond)

Percentage ionic character of a bond betweenPercentage ionic character of a bond betweenPercentage ionic character of a bond betweenPercentage ionic character of a bond betweenelements A and B,elements A and B,elements A and B,elements A and B,

(A being more electronegative) = {1(A being more electronegative) = {1(A being more electronegative) = {1(A being more electronegative) = {1---- exp[exp[exp[exp[----(0.25)(X(0.25)(X(0.25)(X(0.25)(XAAAA----

XXXXBBBB))))2222]} X 100]} X 100]} X 100]} X 100


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Covalent bonds are less dense than the Ionic/Metallic bonds,Covalent bonds are less dense than the Ionic/Metallic bonds,Covalent bonds are less dense than the Ionic/Metallic bonds,Covalent bonds are less dense than the Ionic/Metallic bonds,because Covalent bonds are directionalbecause Covalent bonds are directionalbecause Covalent bonds are directionalbecause Covalent bonds are directional

and they cannot pack together in as dense a manner, yielding a lower mass densityand they cannot pack together in as dense a manner, yielding a lower mass densityand they cannot pack together in as dense a manner, yielding a lower mass densityand they cannot pack together in as dense a manner, yielding a lower mass density


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He-

Ne-

Ar-

Kr

F4.0

Cl3.0

Br

Li1.0

Na0.9

K

H2.1

Be1.5

Mg1.2

Ca Ti Cr Fe Ni Zn As

SiC

C(diamond)

H2O

C2.5

H2

Cl2

F2

Si1.8

Ga Ge

O2.0

columnIVA

EXAMPLES: COVALENT BONDING

Molecules with nonmetals Molecules with metals and nonmetals Elemental solids (RHS of Periodic Table)

Compound solids (aboutcolumn IVA)

-

Xe-

Rn-

.

I2.5

At2.2

.

Rb0.8

Cs0.7

Fr0.7

.

Sr1.0

Ba0.9

Ra0.9

. 1.6 . 1.8 1.8 ..

GaAs

.

Sn1.8

Pb1.8


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F0RMATION OF COVALENT BOND:1.SHARING ELECTRONS BETWEEN ATOMS OF SAME TYPE, eg: H2,Cl2,O2 etc

2.SHARING ELECTRONS BETWEEN ATOMS OF DIFFERENT KINDS,

eg:H20,CH4,HCL etc


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Arises from a sea ofdonated valence electrons(1, 2, or 3 from each atom).

+ + +

METALLIC BONDING

Primary bond for metals and their alloys

+ + +

+ + +

Metal is a network of ions in a sea of electrons,Metal is a network of ions in a sea of electrons,Metal is a network of ions in a sea of electrons,Metal is a network of ions in a sea of electrons,with the electron sea providing the binding force which holds the metal ions togetherwith the electron sea providing the binding force which holds the metal ions togetherwith the electron sea providing the binding force which holds the metal ions togetherwith the electron sea providing the binding force which holds the metal ions together


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Electrons are shared by all atoms,that is they are delocalized throughout the crystalElectrons are shared by all atoms,that is they are delocalized throughout the crystalElectrons are shared by all atoms,that is they are delocalized throughout the crystalElectrons are shared by all atoms,that is they are delocalized throughout the crystal


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Arises from interaction between dipoles

Fluctuating dipoles

HH HH

H2

H2

secondary

ex: liquid H2asymmetric electron

clouds

+ - + -secondary

bonding

SECONDARY BONDING

Permanentdipoles-molecule induced

+ - secondarybonding

+ -

H Cl H Clsecondarybonding

secondarybonding

-general case:

-ex: liquid HCl

-ex: polymerCoulombic interactionCoulombic interactionCoulombic interactionCoulombic interaction

between +ve end of one dipolebetween +ve end of one dipolebetween +ve end of one dipolebetween +ve end of one dipoleandandandand ve region of the adjacent dipoleve region of the adjacent dipoleve region of the adjacent dipoleve region of the adjacent dipole

Strength of these types of forces decreasesStrength of these types of forces decreasesStrength of these types of forces decreasesStrength of these types of forces decreaseswith increase in intermolecular separationwith increase in intermolecular separationwith increase in intermolecular separationwith increase in intermolecular separation


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Polar moleculePolar moleculePolar moleculePolar molecule----Induced dipole bondsInduced dipole bondsInduced dipole bondsInduced dipole bonds

Polar HCl MoleculePolar HCl MoleculePolar HCl MoleculePolar HCl Molecule

ATTRACTIVE FORCES between TEMPORARY DIPOLE and INDUCED DIPOLE are known asATTRACTIVE FORCES between TEMPORARY DIPOLE and INDUCED DIPOLE are known asATTRACTIVE FORCES between TEMPORARY DIPOLE and INDUCED DIPOLE are known asATTRACTIVE FORCES between TEMPORARY DIPOLE and INDUCED DIPOLE are known as

Van der waals forcesVan der waals forcesVan der waals forcesVan der waals forcesFLUCTUATING DIPOLE BONDS ARE BETWEEN NON POLAR ATOMS/MOLECULES

Molecule develops aMolecule develops aMolecule develops aMolecule develops aTEMPORARY DIPOLETEMPORARY DIPOLETEMPORARY DIPOLETEMPORARY DIPOLE

(INSTANTANEOUS DIPOLE(INSTANTANEOUS DIPOLE(INSTANTANEOUS DIPOLE(INSTANTANEOUS DIPOLE)


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HYDROGEN BONDING

EXISTS IN THE MOLECULES THAT HAVE HYDROGEN BONDEDTO NITROGEN, OXYGEN or FLUORINE

ELECTROSTATIC FORCE OF ATTRACTION EXISTS BETWEEN THECOVALENTLY BONDED HYDROGEN ATOM OF ONE MOLECULE ANDTHE ELECTRONEGATIVE ATOM OF THE OHER MOLECULE

+ - + ---------H F ------------H F-----------

Hydrogen Bond Covalent Bond* H atom must be bonded to a highly electronegative atom

* Size of electronegative atom should be small(HCl does notcontain a Hydrogen bond,because size of Cl is large)It coexists with the covalent bond ,weaker than primary bonds

but stronger than secondary bondsM.P and B.P is high compared to other intermolecular bondings


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Type

Ionic

Covalent

Bond Energy

Large!

Variablelarge-Diamond

-

Comments

Nondirectional (ceramics)

Directionalsemiconductors, ceramics

SUMMARY: BONDING

Metallic

Secondary

Variablelarge-Tungstensmall-Mercury

smallest

Nondirectional (metals)

Directionalinter-chain (polymer)

inter-molecular

PROPERTIES FROM


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Bond length, r

Bond energy, Eo

FF

r

Melting Temperature, Tm

Energy (r)

ro

PROPERTIES FROM

BONDING: TM

Eo=

bond energy

Energy (r)

ror

unstretched length

r

larger Tm

smaller Tm

Tm is larger if Eo is larger.

PROPERTIES FROM BONDING E


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Elastic modulus, E

crosssectionalarea Ao

L

length, Lo

F

undeformed

deformed

LFAo= E Lo

Elastic modulus

PROPERTIES FROM BONDING: E

~ curva ure a ro

r

larger Elastic Modulus

smaller Elastic Modulus

Energy

rounstretched length

E is larger if Eo is larger.


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Coefficient of thermal expansion,

L

length, Lo

unheated, T1

heated, T2

= (T2-T1)

LLo

coeff. thermal expansion

PROPERTIES FROM BONDING:

~ symmetry at ro

is larger if Eo is smaller.r

smaller

larger

Energy

ro

Small dimensional alterationsfor changes in temperature


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Ceramics(Ionic & covalent bonding):

Metals

(Metallic bonding):

Large bond energylarge Tmlarge Esmall

Variable bond energymoderate Tmmoderate E

SUMMARY: PRIMARY BONDS

Polymers(Covalent & Secondary):

secondarybonding

moderate

Directional PropertiesSecondary bonding dominates

small Tsmall Elarge


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Problems:2.13 to 2.18

2.13 The net Potential Energy bet. two adjacent ions,E N = EA + ER= - A/r + B/r

n ------(1)By differentiating EN w.r.t r,

dEN

/dr = - A/r2 + nB/rn+1 = 0(r is minimum at E0 = r0r0= equilibrium inter-ionic spacing),or, A/ r2 = nB/rn+1, A/nB = r2/rn+1, A/nB = r1-n,

Therefore, r0 = (A/nB)1/1-n-----(2) ,(A=1.436,B=7.32 x 10-6,n=8)

Putting these values n the above expression,r0= 0.236nm.

Substituting the expression for r0from (2) in (1) and solving forE (= E0 )and solving it, we get, E0 = -5.32ev


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2.15 r0 = (A/nB)1/1-n ,

E 0 = - A/(A/nB)1/1-n + B/(A/nB)n/1-n

Thus we have two simultaneous equations with twounknowns (A and B),substituting the values of r0 and E0

in terms of n, we get,0.35nm = (A/10B)1/1-10

-6.13ev = - A/(A/10B)1/1-10 + B/(A/nB)10/1-10

simultaneous solutions to these two equations give,A=2.38 and B=1.88X10-5,

EA =- A/r = -2.38/r

ER = B/rn = 1.88X10-5 / r10

ch-2 compatibility mode

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