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Materials Science ConceptsMATS-535 Electronics and Photonics Materials

Scope

a – Atomic Structure and Atomic Number

b – Bonding and Type of Solids

Dr. Vladimir GavrilenkoNorfolk State University

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Atomic Structure of Materials

•Basic building blocks of matter•Classic vs. quantum treatments•Models of atoms•Bohr model

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S tab le o rb it h a s rad iu s ro

ro

v

­e

The planetary model of the hydrogen atom in which the negativelycharged electron orbits the positively charged nucleus.

Bohr Atom

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The shell model of the atom in which the electrons are confined tolive within certain shells and in subshells within shells.

N uc leu s

2 s2 p

1 sK

L

L sh e l l w i thtw o su b sh e l ls

1 s 22 s 22 p 2 o r [H e ]2 s 22 p 2

Shell Model. Carbon Atom

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Ionization Energy and Electron Affinity

Ionization Energy – Smallest energy required to remove an electron from neutral atomElectron Affinity – Energy that is needed (or released) when one adds an electron to a neutral atomH

Na

H+

0

-5.1 eV

-13.6 eV

IE

EA

H-

EA(H-)=0.7541 eV required energyEA (Cl-)=-349. kJ/mol =-3.62 eV released energy

1Takahashi et al Rev. Sci. Instr. 71, 1101 (2000)

-12.98 eV Cl

1 eV = 96.4 kJ/mol

Cl-

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Atomic Scale Units

0

00

2

34

19

110

31

4

1

2.274

10054.12

106.1

A529.01029.5

101.9

C

eVr

eE

sJh

Ce

mr

kgm

h

o

e

Fundamental au:

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Atomic Mass and Mole

Atomic mass:

23

27

10022.6

1066054.112

1

A

Cat

N

kgmm

Avogadro’s number:

One mole of a substance has a mass equal to its atomic (molecular) mass in grams

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In tera tom ic sep ara tio n , r

+

Attra

ctio

nR

epul

sion

0

F A = A ttra c tiv e fo rc e

FR = R epu ls iv e fo rce

FN = N et fo rc e

ro

r = M olecu le

S ep arated atom s

r o

(a) Force vs r

E A = A ttra c tiv e PE

E R = R epu lsiv e PE

E = N et PE

E oro

(b ) Potential energy vs r

Fo

rce

+

Attr

act

ion

Rep

uls

ion

0

Po

ten

tia

lEn

erg

y,E(r)

r

(a) Force vs interatomic separation and (b) Potential energy vsinteratomic separation.

Atomic Bonding

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Atomic Bonding

min

,0

,0

tottot

tottot

RAtot

EE

dr

dEF

FFF

Equilibrium conditions:

Bond energy is an energy that is required to separate to particles

Why the materials are stable?What prevents from the collapse?

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1 s

E le c tro n sh e l l

C o v a le n t b o n d

H -a tom H -a tom

H -H M o le c u le

1

1

2

2

12

1 s

Formation of a covalent bond between two H atoms leads to the H2molecule. Electrons spend majority of their time between the twonuclei which results in a net attraction between the electrons and thetwo nuclei which is the origin of the covalent bond .

Covalent Bonding

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H

109 .5 °

C

HH

H(c)

H

H H

H

L sh e ll

K sh ell

C ova len t b ond

C

(a)

C

H

H H

H

co va len tbo n ds

(b)

(a ) C ov a len t bo nd in g in m eth an e , C H 4 , in v o lv e s fou r h yd rog ena tom s sh arin g e le c tro n s w ith o n e carb on a tom . E ach co va len t bo ndh as tw o sh a red e lec tro n s . T h e fou r bon d s a re id en tic a l and rep e le ach o th er.(b ) S ch em a tic sk e tch o f C H 4 on pap e r.(c ) In th re e d im en s io n s , d u e to sym m e try, th e bon d s a re d irec tedtow a rd s th e co rn e rs o f a te trah ed ron .

Methane Molecule

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The diamond crystal is a covalently bonded network of carbon atoms.Each carbon atom is bonded covalently to four neighbors forming aregular three dimensional pattern of atoms which constitutes thediamond crystal.

Diamond Crystal

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F re e v a len c ee le c tro n s fo rm in g a n

e lec tro n g as

P o s i tiv e m e ta lio n c o re s

In metallic bonding the valence electrons from the metal atomsform a "cloud of electrons" which fills the space between themetal ions and "glues" the ions together through the coulombicattraction between the electron gas and positive metal ions.

Metallic Bond

FCC Copper:

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3 p3 s

C losed K and L shells

3 s

C losed K and L shells

(a )

3 p3 sFA

r

FA

(b )

ro

(c )

The formation of an ionic bond between Na and Cl atoms in NaCl.The attraction is due to coulombic forces.

NaCl

Na+Cl-

Na+

Cl-

Ionic Bond

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(b )

C l­N a+ Na+ Na+C l­ C l­

C l­N a+ N a+ N a+C l­C l­

C l­N a+ N a+ Na+C l­ C l­

C l­N a+ N a+ N a+C l­C l­

C l­N a+ N a+ Na+C l­ C l­

C l­N a+ N a+ Na+C l­C l­

(a )

(a) A schematic illustration of a cross section from solid NaCl.NaCl solid is made of Cl and Na+ ions arranged alternatingly sothat the oppositely charged ions are closest to each other and attracteach other. There are also repulsive forces between the like-ions. Inequilibrium the net force acting on any ion is zero.(b) Solid NaCl.

Simple Cubic Structure

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C l N a +

ro = 0 .2 8 nm

6

­ 6

0

­ 6 .3

0 .2 8 nm

Potent

iale

nerg

yE(r),

eV/(io

n-pa

ir)

S ep a ra tio n , r1 .5 eV

r =

C l N ar =

N a +C l

Sketch of the potential energy per ion-pair in solid NaCl. Zeroenergy corresponds to neutral Na and Cl atoms infinitely separated.

Co

hes

ive

en

erg

y

Potential Energy Plot

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A B

A B (b)

HC l

(a )

(c)

(a) A permanently polarized molecule is called a an electric dipolemoment.(b) Dipoles can attract or repel each other depending on their relativeorientations.(c) Suitably oriented dipoles attract each other to form van der Waalsbonds.

Primary and Secondary Bonds

Primary bonds:-Metallic-Ionic-CovalentSecondary bonds:-Van der Waals type-Hydrogen type

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The origin of van der Waals bonding between water molecules.(a) The H2O molecule is polar and has a net permanent dipolemoment.(b) Attractions between the various dipole moments in water givesrise to van der Waals bonding.

(b)

H

O

H

(a)

Van der Waals Bonds

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T im e ave raged e lec tron (n egativ e charg e)d is trib u tion

C losed L Shell

Ion ic core(N ucleu s + K -sh ell)

N e

In stan taneou s e lec tron (n ega tiv e ch arg e)d istrib u tio n flu c tu a te s about the nuc leu s.

A B

Synchronized fluctuationsof the electrons

van der W aals force

Induced dipole-induced dipole interaction and the resulting van derWaals force.

Van der Waals Bonds

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