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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
2
Atomic Structure of Materials
•Basic building blocks of matter•Classic vs. quantum treatments•Models of atoms•Bohr model
3
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
4
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
5
6
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-
7
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:
8
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
9
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
10
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?
11
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
12
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
14
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
16
(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
17
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
18
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
19
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
20
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
21