ch02-materials science

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Chapter 2 - 1

Properties depend on

- arrangement of atoms

- interactions between atoms

Study Bonding:

• What promotes bonding?• What types of bonds are there?

• What properties are inferred from bonding?

CHAPTE 2!

"#$%&$' A$% P#PET&E(



Chapter 2 - 2

Atomic (tr)ct)re *+reshman Chem,

• atom . e/ectrons . 0,11 1-31

4gprotons ne)trons

• n)c/e)s of atom! 5si6e of a point on a page7 -8 فر

• atomic n)mber 9 $o, of protons in n)c/e)s of atom 9 $o, of e/ectrons of ne)tra/ species

A :9; atomic mass )nit 9 am) 9 1<12 mass of 12C

Atomic wt 9 wt of =,23 123 mo/ec)/es or atoms

>nit 1 am)<atom 9 1g<mo/

C 12,11

H 1, etc,

} 1,=@ 1-2@ 4g



Chapter 2 - 3

Atomic (tr)ct)re

• a/ence e/ectrons! in the o)ter-she//

• determine a// of the fo//owing properties

1 Chemica/! reactiBity

2 E/ectrica/! cond)ctiBity

3 Therma/! cond)ctiBity

#ptica/! transmittance



Chapter 2 -

E/ectronic (tr)ct)re - eBiew

• Electrons have wavelike and particulate properties. . This means that e/ectrons are in orbita/s defined by a

probabi/ity,

. Each orbita/ at discrete energy /eBe/ determined by

D)ant)m n)mbers,

)ant)m F %esignation

n 9 principa/ *energy /eBe/-she// K G LG M G N G O *1G 2G 3G etc,

l 9 s)bsidiary *orbita/s sG pG d G f *G 1G 2G 3GG n -1

ml 9 magnetic *direction in space 1G 3G IG @ *-l to Jl

ms 9 spin KG -K



Chapter 2 - I

E/ectron Energy (tates

1s

2s2 p

K -she// n 9 1

L-she// n 9 2

3s3 p M -she// n 9 3

3d

s

pd

Energy

N -she// n 9

• haBe discrete energy states• tend to occ)py /owest aBai/ab/e energy state,

E/ectrons,,,



Chapter 2 - =

• Why? a/ence *o)ter she// )s)a//y not fi//ed comp/ete/y,

• Lost e/ements! E/ectron config)ration not stab/e,

(>EM #+ ENELE$T( - eBiew

E/ectron config)ration

*stab/e

,,,

,,,

1s22s22 p =3s23 p = *stab/e,,,

1s22s22 p =3s23 p =3d 1 s2 p= *stab/e

Atomic F

1,,,

3=

E/ement1s1 1Hydrogen

1s22He/i)m

1s22s1 3Nithi)m

1s22s2"ery//i)m

1s22s22 p 1I"oron

1s22s22 p 2=Carbon,,,

1s22s22 p = *stab/e1$eon1s22s22 p =3s111(odi)m

1s22s22 p =3s2 12Lagnesi)m

1s22s22 p =3s23 p 113 A/)min)m,,,

Argon,,,

Orypton



Chapter 2 - @

E/ectron Config)rations

• a/ence e/ectrons . those in )nfi//ed she//s• +i//ed she//s more stab/e• a/ence e/ectrons are most aBai/ab/e for bonding and

tend to contro/ the chemica/ properties

• Primary Bonding! &onicG CoBa/ent and Leta//ic

• eamp/e! C *atomic n)mber 9 =

1s2 2s2 2 p2

Ba/ence e/ectrons



Chapter 2 -

E/ectronic Config)rationse! +e - atomic F 9 2=

Ba/ence

e/ectrons

1s

2s2 p

K -she// n 9 1

L-she// n 9 2

3s3 p M -she// n 9 3

3d

s

pd

Energy

N -she// n 9

1s2 2s2 2 p= 3s2 3 p= 3d = s2



Chapter 2 - 0

The Periodic Tab/e• Co/)mns! (imi/ar a/ence (tr)ct)re

E/ectropositiBe e/ements!

eadi/y giBe )p e/ectrons

to become J ions,

E/ectronegatiBe e/ements!

eadi/y acD)ire e/ectrons

to become - ions,

g i B e

) p 1

e

g i B e

) p

2 e

g i B e

) p

3 e

i n e r t g a s

e s

a c c e p t 1 e

a c c e p t 2 e

#

(e

Te

Po At

&

"r

He

$e

Ar

Or

e

n

+

C/(

Ni "e

H

$a Lg

"aCs

a+r

CaO (c

(r b M



Chapter 2 - 1

• anges from ,@ to ,G

(ma//er e/ectronegatiBity Narger e/ectronegatiBity

• Narge Ba/)es! tendency to acD)ire e/ectrons,

E/ectronegatiBity



Chapter 2 - 11

&onic bond . meta/ J nonmeta/

donates accepts

e/ectrons e/ectrons%issimi/ar e/ectronegatiBities

e! Lg# Lg 1s2 2s2 2 p= 3s2 # 1s2 2s2 2 pC

:$e; 3s2

Lg2J 1s2 2s2 2 p= #2- 1s2 2s2 2 p=

:$e; :$e;

1s22s22 p = *stab/e1$eon



Chapter 2 - 12

• #cc)rs between J and - ions,

• eD)ires e/ectron transfer,• Narge difference in e/ectronegatiBity reD)ired,

• Eamp/e! $aC/

&onic "onding

$a *meta/)nstab/e

C/ *nonmeta/)nstab/e

e/ectron

+ -Co)/ombic

Attraction

$a *cationstab/e

C/ *anionstab/e



Chapter 2 - 13

• Predominant bonding in Ceramics

Eamp/es! &onic "onding

'iBe )p e/ectrons AcD)ire e/ectrons

$aC/

Lg#

Ca+2CsC/



Chapter 2 - 1

C! has Ba/ence e-

G needs more

H! has 1 Ba/ence e -G

needs 1 more

E/ectronegatiBities are comparab/e,

CoBa/ent "onding• simi/ar e/ectronegatiBity ∴ share e/ectrons

• bonds determined by Ba/ence . s Q p orbita/sdominate bonding

• Eamp/e! CHshared e/ectronsfrom carbon atom

shared e/ectrons

from hydrogenatoms

H

H

H

H

C

CH



Chapter 2 - 1I

Primary "onding

• Leta//ic "ond -- de/oca/i6ed as e/ectron c/o)d

• &onic-CoBa/ent Lied "onding

R ionic character 9

where X A Q X " are Pa)/ing e/ectronegatiBities

R1*1−e−

* X A− X " 2

C

ionic@,2R*1R-e1character ionicR

3,1I,3*

2

=

−=

−−

E! Lg# X Lg 9 1,3

X # 9 3,I



Chapter 2 - 1=

Arises from interaction between dipo/es

• Permanent dipo/es-mo/ec)/e ind)ced

• +/)ct)ating dipo/es

-genera/ case!

-e! /iD)id HC/

-e! po/ymer

Adapted from +ig, 2,1G

Callister 7e.

(EC#$%AM "#$%&$'

asymmetric e/ectron

c/o)ds

J - J -

secondarybonding

HH HH

H2 H2

secondarybonding

e! /iD)id H2

H C/ H C/secondary

bonding

secondarybonding

J - J -

secondary bondings e c o n d ar y b o n d i n g



Chapter 2 - 1@

Type

&onic

CoBa/ent

Leta//ic

(econdary

"ond Energy

Narge8

ariab/e

/arge-%iamondsma//-"ism)th

ariab/e/arge-T)ngstensma//-Lerc)ry

sma//est

Comments

$ondirectiona/ *ceramics

%irectiona/

*semicond)ctorsG ceramicspo/ymer chains

$ondirectiona/ *meta/s

%irectiona/

inter-chain *po/ymer

inter-mo/ec)/ar

()mmary! "onding



Chapter 2 - 1

&nteractions "etween Atoms

J-

J-

r

J-

J-

(pacing *r

Atomic adi)s *

+ar Atoms! Attraction C/ose Atoms! Repulsion

ED)i/ibri)m spacing 9 r o

r o 9 2

J

-

J

-

Dynamic Equilirium



Chapter 2 - 10



Chapter 2 - 2

"onding C)rBe



Chapter 2 - 21

"onding C)rBe

• Energy . minim)m energy most stab/e . Energy ba/ance of attractiBe and rep)/siBe terms

AttractiBe energy E A

$et energy E N

ep)/siBe energy E R

&nteratomic separation r

r A

nr B

E N 9 E A + E R 9 −−r o



Chapter 2 - 22

"onding - Estimations

• Estimation of "onding Energy *E o and ED)i/ibri)m (pacing *r o• 'iBen!

• "onding occ)rs at energy minim)m

• At minim)m! %eriBatiBe dE<dr 9 g*r 9

• (o/Be g*r 9 for r r o

• ()bstit)te r9r o in the Energy EDn!

• 'et Eo 9 E *r9r o

• Atomic radi)s 9 r o<2E o 9

5bond energy7

Energy

r o r

r A

nr B

E 9 certain f(r) e.g. E 9 −

!or many atoms" r o is appro#imately $.% nm.



Chapter 2 - 23

• "ond /engthG r

• "ond energyG E o

• Le/ting Temperat)reG m

m is /arger if E o is /arger,

Properties +rom "onding! m

r o r

Energy

r

/arger m

sma//er m

E o 9

5bond energy7

Energy

r o

r

)nstretched /ength



Chapter 2 - 2

• Coefficient of therma/ epansionG α

• α S symmetry at r o

α is /arger if E o is sma//er,

Properties +rom "onding ! α

=α * 2 - 1∆L

Lo

Coefficient of therma/ epansion

∆L

/engthG Lo

)nheatedG 1

heatedG 2

r or

(ma//er α

Narger α

Energy

)nstretched /ength

E !

E !



Chapter 2 - 2I

Ceramics

*&onic Q coBa/ent bonding!

Leta/s

*Leta//ic bonding!

Po/ymers

*CoBa/ent Q (econdary!

Narge bond energy

/arge m/arge E

sma// α

ariab/e bond energymoderate mmoderate E

moderate α

%irectiona/ Properties

(econdary bonding dominates sma// m sma// E

/arge α

()mmary! Primary "onds

s e c o n d ar y b o n d i n g

Bonding in Solids & 'iquids & (ases



Chapter 2 - 2=

Reading! +oc)s on Atomic "onding in (o/ids

)ore Prolems!

2,@G 2,G 2,12G 2,13G

2,1@G 2,10G 2,21 *Ca//ister 3rd Addition

*ui+! $et C/ass

A$$#>$CELE$T(



Chapter 2 - 2@

)i6

Energy

Atomic Spacing r

A"

c

Rank materials A" B and ) according to1, &ncreasing me/ting temperat)re

2, %ecreasing bonding energy

3, &ncreasing Atomic adi)s

, &ncreasing coefficient of therma/ epansion



Chapter 2 - 2

)i6

Energy

Atomic Spacing r

A

B

c

Rank materials A" B and ) according to1, &ncreasing me/ting temperat)re

2, %ecreasing bonding energy

3, &ncreasing Atomic adi)s

, &ncreasing coefficient of therma/ epansion

ch02-materials science

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