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eq;

1. (1)
Atomic Structure and
Interatomic Bonding

2. Nucleus: Z = # protons
2
orbital electrons:
n = principal
quantum number
n=3
21
= 1 for hydrogen to 94 for plutonium
N = # neutrons
Atomic mass A ≈ Z + N
Adapted from Fig. 2.1,
Callister 6e.
BOHR ATOM

3. • have discrete energy states
• tend to occupy lowest available energy state.
3
I
n
c
r
e
a
s
i
n
g

e
n
e
r
g
y
n=1
n=2
n=3
n=4
1s
2s
3s
2p
3p
4s
4p
3d
Electrons...
Adapted from Fig. 2.5,
Callister 6e.
ELECTRON ENERGY STATES

4. 4
• have complete s and p subshells
• tend to be unreactive.
Stable electron configurations...
Z Element Configuration
2 He 1s
2

10 Ne 1s
2
2s
2
2p
6

18 Ar 1s
2
2s
2
2p
6
3s
2
3p
6
36 Kr 1s
2
2s
2
2p
6
3s
2
3p
6
3d
10
4s
2
4p
6
Adapted from Table 2.2,
Callister 6e.
STABLE ELECTRON CONFIGURATIONS

5. 5
• Why? Valence (outer) shell usually not filled completely.
• Most elements: Electron configuration not stable.
Element
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
...
Neon
Sodium
Magnesium
Aluminum
...
Argon
...
Krypton
Atomic #
1
2
3
4
5
6

10
11
12
13

18
...
36
Electron configuration
1s
1
1s
2
(stable)
1s
22s
1
1s
22s
2
1s
22s
22p
1
1s
22s
22p
2
...
1s
22s
22p
6
(stable)
1s
22s
22p
63s
1
1s
22s
22p
63s
2
1s
22s
22p
63s
23p
1
...
1s
22s
22p
63s
23p
6
(stable)
...
1s
22s
22p
63s
23p
63d
104s
24
6
(stable)
Adapted from Table 2.2,
Callister 6e.
SURVEY OF ELEMENTS

6. 6
• Columns: Similar Valence Structure
Electropositive elements:
Readily give up electrons
to become + ions.
Electronegative elements:
Readily acquire electrons
to become - ions.
He
Ne
Ar
Kr
Xe
Rn
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

g
i
v
e

u
p
1
e

g
i
v
e

u
p
2
e

g
i
v
e

u
p

3
e

F Li Be
Metal
Nonmetal
Intermediate
H
Na Cl
Br
I
At
O
S Mg
Ca
Sr
Ba
Ra
K
Rb
Cs
Fr
Sc
Y
Se
Te
Po
Adapted
from Fig. 2.6,
Callister 6e.
THE PERIODIC TABLE

7. METALS

8. CERAMICS

9. POLYMERS

10. SEMICONDUCTOR

12. 7
• Ranges from 0.7 to 4.0,
Smaller electronegativity Larger electronegativity
He
-
Ne
-
Ar
-
Kr
-
Xe
-
Rn
-
F
4.0
Cl
3.0
Br
2.8
I
2.5
At
2.2
Li
1.0
Na
0.9
K
0.8
Rb
0.8
Cs
0.7
Fr
0.7
H
2.1
Be
1.5
Mg
1.2
Ca
1.0
Sr
1.0
Ba
0.9
Ra
0.9
Ti
1.5
Cr
1.6
Fe
1.8
Ni
1.8
Zn
1.8
As
2.0
• Large values: tendency to acquire electrons.
Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the
Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell
University.
ELECTRONEGATIVITY

13. Na (metal)
unstable
Cl (nonmetal)
unstable
electron
+ -
Coulombic
Attraction
Na (cation)
stable
Cl (anion)
stable
8
• Occurs between + and - ions.
• Requires electron transfer.
• Large difference in electronegativity required.
• Example: NaCl
IONIC BONDING

14. 9
• Predominant bonding in Ceramics
Give up electrons Acquire electrons
He
-
Ne
-
Ar
-
Kr
-
Xe
-
Rn
-
F
4.0
Cl
3.0
Br
2.8
I
2.5
At
2.2
Li
1.0
Na
0.9
K
0.8
Rb
0.8
Cs
0.7
Fr
0.7
H
2.1
Be
1.5
Mg
1.2
Ca
1.0
Sr
1.0
Ba
0.9
Ra
0.9
Ti
1.5
Cr
1.6
Fe
1.8
Ni
1.8
Zn
1.8
As
2.0
CsCl
MgO
CaF2
NaCl
O
3.5
Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the
Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell
University.
EXAMPLES: IONIC BONDING

15. 10
• Requires shared electrons
• Example: CH4
C: has 4 valence e,
needs 4 more
H: has 1 valence e,
needs 1 more
Electronegativities
are comparable.
shared electrons
from carbon atom
shared electrons
from hydrogen
atoms
H
H
H
H
C
CH4
Adapted from Fig. 2.10, Callister 6e.
COVALENT BONDING

16. 11
• Molecules with nonmetals
• Molecules with metals and nonmetals
• Elemental solids
• Compound solids (about column IVA)
He
-
Ne
-
Ar
-
Kr
-
Xe
-
Rn
-
F
4.0
Cl
3.0
Br
2.8
I
2.5
At
2.2
Li
1.0
Na
0.9
K
0.8
Rb
0.8
Cs
0.7
Fr
0.7
H
2.1
Be
1.5
Mg
1.2
Ca
1.0
Sr
1.0
Ba
0.9
Ra
0.9
Ti
1.5
Cr
1.6
Fe
1.8
Ni
1.8
Zn
1.8
As
2.0
SiC
C(diamond)
H2O
C
2.5
H2
Cl2
F2
Si
1.8
Ga
1.6
GaAs
Ge
1.8
O
2.0
c
o
l
u
m
n

I
V
A
Sn
1.8
Pb
1.8
Adapted from Fig. 2.7, Callister 6e. (Fig. 2.7 is
adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright
1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.
EXAMPLES: COVALENT BONDING

17. 12
• Arises from a sea of donated valence electrons
(1, 2, or 3 from each atom).
• Primary bond for metals and their alloys
+ + +
+ + +
+ + +
Adapted from Fig. 2.11, Callister 6e.
METALLIC BONDING

18. 13
Arises from interaction between dipoles
• Permanent dipoles-molecule induced
• Fluctuating dipoles
+-
secondary
bonding
+-
HCl HCl
secondary
bonding
secondary bonding
HH HH
H2 H2
secondary
bonding
ex: liquid H2asymmetric electron
clouds
+- +-
secondary
bonding
-general case:
-ex: liquid HCl
-ex: polymer
Adapted from Fig. 2.13, Callister 6e.
Adapted from Fig. 2.14,
Callister 6e.
Adapted from Fig. 2.14,
Callister 6e.
SECONDARY BONDING

19. 14
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large!
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
smallest
Comments
Nondirectional (ceramics)
Directional
semiconductors, ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
SUMMARY: BONDING

20. 15
• Bond length, r
• Bond energy, Eo
F
F
r
• Melting Temperature, Tm
Eo=
“bond energy”
Energy (r)
ro
r
unstretched length
r
larger Tm
smaller Tm
Energy (r)
ro
Tm is larger if Eo is larger.
PROPERTIES FROM BONDING: T
M

21. 16
• Elastic modulus, E
• E ~ curvature at ro
cross
sectional
area Ao
L
length, Lo
F
undeformed
deformed
L F
Ao
= E
Lo
Elastic modulus
r
larger Elastic Modulus
smaller Elastic Modulus
Energy
ro
unstretched length
E is larger if Eo is larger.
PROPERTIES FROM BONDING: E

22. 17
• Coefficient of thermal expansion, 
•  ~ symmetry at ro
 is larger if Eo is smaller.
L
length, Lo
unheated, T1
heated, T2

= (T2-T1)
L
Lo
coeff. thermal expansion
r
smaller 
larger 
Energy
ro
PROPERTIES FROM BONDING: 

23. 18
Ceramics
(Ionic & covalent bonding):
Metals
(Metallic bonding):
Polymers
(Covalent & Secondary):
secondary bonding
Large bond energy
large Tm
large E
small 
Variable bond energy
moderate Tm
moderate E
moderate 
Directional Properties
Secondary bonding dominates
small T
small E
large 
SUMMARY: PRIMARY BONDS

24. 2
• Non dense, random packing
• Dense, regular packing
Dense, regular-packed structures tend to have
lower energy.
Energy
r
typical neighbor
bond length
typical neighbor
bond energy
Energy
r
typical neighbor
bond length
typical neighbor
bond energy
ENERGY AND PACKING

25. • atoms pack in periodic, 3D arrays
• typical of:
3
Crystalline materials...
-metals
-many ceramics
-some polymers
• atoms have no periodic packing
• occurs for:
Noncrystalline materials...
-complex structures
-rapid cooling
Si Oxygen
crystalline SiO2
noncrystalline SiO2"Amorphous" = Noncrystalline
Adapted from Fig. 3.18(b),
Callister 6e.
Adapted from Fig. 3.18(a),
Callister 6e.
MATERIALS AND PACKING

26. 4
• tend to be densely packed.
• have several reasons for dense packing:
-Typically, only one element is present, so all atomic
radii are the same.
-Metallic bonding is not directional.
-Nearest neighbor distances tend to be small in
order to lower bond energy.
• have the simplest crystal structures.
We will look at three such structures...
METALLIC CRYSTALS

27. 5
• Rare due to poor packing (only Po has this structure)
• Close-packed directions are cube edges.
• Coordination # = 6
(# nearest neighbors)
(Courtesy P.M. Anderson)
SIMPLE CUBIC STRUCTURE (SC)

28. 6
APF =
Volume of atoms in unit cell*
Volume of unit cell
*assume hard spheres
• APF for a simple cubic structure = 0.52
APF =
a
3
4
3
(0.5a)
3
1
atoms
unit cell
atom
volume
unit cell
volume
close-packed directions
a
R=0.5a
contains 8 x 1/8 =
1 atom/unit cell
Adapted from Fig. 3.19,
Callister 6e.
ATOMIC PACKING FACTOR

29. • Coordination # = 8
7
Adapted from Fig. 3.2,
Callister 6e.
(Courtesy P.M. Anderson)
• Close packed directions are cube diagonals.
--Note: All atoms are identical; the center atom is shaded
differently only for ease of viewing.
BODY CENTERED CUBIC STRUCTURE
(BCC)

30. a
R
8
• APF for a body-centered cubic structure = 0.68
Close-packed directions:
length = 4R
= 3 a
Unit cell contains:
1 + 8 x 1/8
= 2 atoms/unit cell
Adapted from
Fig. 3.2,
Callister 6e.
ATOMIC PACKING FACTOR: BCC
APF =
a
3
4
3
( 3a/4)
3
2
atoms
unit cell
atom
volume
unit cell
volume

31. 9
• Coordination # = 12
Adapted from Fig. 3.1(a),
Callister 6e.
(Courtesy P.M. Anderson)
• Close packed directions are face diagonals.
--Note: All atoms are identical; the face-centered atoms are shaded
differently only for ease of viewing.
FACE CENTERED CUBIC STRUCTURE
(FCC)

32. APF =
a
3
4
3
( 2a/4)
3
4
atoms
unit cell
atom
volume
unit cell
volume
Unit cell contains:
6 x 1/2 + 8 x 1/8
= 4 atoms/unit cell
a
10
• APF for a body-centered cubic structure = 0.74
Close-packed directions:
length = 4R
= 2 a
Adapted from
Fig. 3.1(a),
Callister 6e.
ATOMIC PACKING FACTOR: FCC

33. 11
• ABCABC... Stacking Sequence
• 2D Projection
A sites
B sites
C sites
BB
B
BB
BB
CC
C
A
A
• FCC Unit Cell
A
B
C
FCC STACKING SEQUENCE

34. 12
• Coordination # = 12
• ABAB... Stacking Sequence
• APF = 0.74
• 3D Projection • 2D Projection
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Adapted from Fig. 3.3,
Callister 6e.
HEXAGONAL CLOSE-PACKED
STRUCTURE (HCP)

35. 13
• Compounds: Often have similar close-packed structures.
• Close-packed directions
--along cube edges.
• Structure of NaCl
(Courtesy P.M. Anderson) (Courtesy P.M. Anderson)
STRUCTURE OF COMPOUNDS: NaCl

36. 14
Example: Copper

nA
V
cN
A
# atoms/unit cell Atomic weight (g/mol)
Volume/unit cell
(cm
3
/unit cell)
Avogadro's number
(6.023 x 10
23
atoms/mol)
Data from Table inside front cover of Callister (see next slide):
• crystal structure = FCC: 4 atoms/unit cell
• atomic weight = 63.55 g/mol (1 amu = 1 g/mol)
• atomic radius R = 0.128 nm (1 nm = 10 cm)-7
Vc = a
3
; For FCC, a = 4R/ 2 ; Vc = 4.75 x 10
-23
cm
3
Compare to actual: Cu = 8.94 g/cm
3
Result: theoretical Cu = 8.89 g/cm
3
THEORETICAL DENSITY, 

37. 15
Element
Aluminum
Argon
Barium
Beryllium
Boron
Bromine
Cadmium
Calcium
Carbon
Cesium
Chlorine
Chromium
Cobalt
Copper
Flourine
Gallium
Germanium
Gold
Helium
Hydrogen
Symbol
Al
Ar
Ba
Be
B
Br
Cd
Ca
C
Cs
Cl
Cr
Co
Cu
F
Ga
Ge
Au
He
H
At. Weight
(amu)
26.98
39.95
137.33
9.012
10.81
79.90
112.41
40.08
12.011
132.91
35.45
52.00
58.93
63.55
19.00
69.72
72.59
196.97
4.003
1.008
Atomic radius
(nm)
0.143
------
0.217
0.114
------
------
0.149
0.197
0.071
0.265
------
0.125
0.125
0.128
------
0.122
0.122
0.144
------
------
Density
(g/cm
3
)
2.71
------
3.5
1.85
2.34
------
8.65
1.55
2.25
1.87
------
7.19
8.9
8.94
------
5.90
5.32
19.32
------
------
Crystal
Structure
FCC
------
BCC
HCP
Rhomb
------
HCP
FCC
Hex
BCC
------
BCC
HCP
FCC
------
Ortho.
Dia. cubic
FCC
------
------
Adapted from
Table, "Charac-
teristics of
Selected
Elements",
inside front
cover,
Callister 6e.
Characteristics of Selected Elements at 20C

38. metals ceramics polymers
16

(
g
/
c
m
3
)
Graphite/
Ceramics/
Semicond
Metals/
Alloys
Composites/
fibers
Polymers
1
2
20
30
Based on data in Table B1, Callister
*GFRE, CFRE, & AFRE are Glass,
Carbon, & Aramid Fiber-Reinforced
Epoxy composites (values based on
60% volume fraction of aligned fibers
in an epoxy matrix). 10
3
4
5
0.3
0.4
0.5
Magnesium
Aluminum
Steels
Titanium
Cu,Ni
Tin, Zinc
Silver, Mo
Tantalum
Gold, W
Platinum
Graphite
Silicon
Glass-soda
Concrete
Si nitride
Diamond
Al oxide
Zirconia
HDPE, PS
PP, LDPE
PC
PTFE
PET
PVC
Silicone
Wood
AFRE*
CFRE*
GFRE*
Glass fibers
Carbon fibers
Aramid fibers
Why?
Metals have...
• close-packing
(metallic bonding)
• large atomic mass
Ceramics have...
• less dense packing
(covalent bonding)
• often lighter elements
Polymers have...
• poor packing
(often amorphous)
• lighter elements (C,H,O)
Composites have...
• intermediate values Data from Table B1, Callister 6e.
DENSITIES OF MATERIAL CLASSES

39. 17
• Some engineering applications require single crystals:
• Crystal properties reveal features
of atomic structure.
(Courtesy P.M. Anderson)
--Ex: Certain crystal planes in quartz
fracture more easily than others.
--diamond single
crystals for abrasives
--turbine blades
Fig. 8.30(c), Callister 6e.
(Fig. 8.30(c) courtesy
of Pratt and Whitney).
(Courtesy Martin Deakins,
GE Superabrasives,
Worthington, OH. Used
with permission.)
CRYSTALS AS BUILDING BLOCKS

40. 18
• Most engineering materials are polycrystals.
• Nb-Hf-W plate with an electron beam weld.
• Each "grain" is a single crystal.
• If crystals are randomly oriented,
overall component properties are not directional.
• Crystal sizes typ. range from 1 nm to 2 cm
(i.e., from a few to millions of atomic layers).
Adapted from Fig. K,
color inset pages of
Callister 6e.
(Fig. K is courtesy of
Paul E. Danielson,
Teledyne Wah Chang
Albany)
1 mm
POLYCRYSTALS

41. 19
• Single Crystals
-Properties vary with
direction: anisotropic.
-Example: the modulus
of elasticity (E) in BCC iron:
• Polycrystals
-Properties may/may not
vary with direction.
-If grains are randomly
oriented: isotropic.
(Epoly iron = 210 GPa)
-If grains are textured,
anisotropic.
E (diagonal) = 273 GPa
E (edge) = 125 GPa
200 m
Data from Table 3.3,
Callister 6e.
(Source of data is
R.W. Hertzberg,
Deformation and
Fracture Mechanics of
Engineering Materials,
3rd ed., John Wiley
and Sons, 1989.)
Adapted from Fig.
4.12(b), Callister 6e.
(Fig. 4.12(b) is
courtesy of L.C. Smith
and C. Brady, the
National Bureau of
Standards,
Washington, DC [now
the National Institute
of Standards and
Technology,
Gaithersburg, MD].)
SINGLE VS POLYCRYSTALS

42. d=n/2sinc
x-ray
intensity
(from
detector)

c
20
• Incoming X-rays diffract from crystal planes.
• Measurement of:
Critical angles, c,
for X-rays provide
atomic spacing, d.
Adapted from Fig.
3.2W, Callister 6e.
X-RAYS TO CONFIRM CRYSTAL STRUCTURE
reflections must
be in phase to
detect signal
spacing
between
planes
d
i
n
c
o
m
i
n
g

X
-
r
a
y
s
o
u
t g
o
i n
g
X
- r a
y
s
d
e
t
e
c
t
o
r



extra
distance
travelled
by wave “2”
“
1
”
“
2
”
“ 1
”
“ 2
”

43. 21
• Atoms can be arranged and imaged!
Carbon monoxide
molecules arranged
on a platinum (111)
surface.
Photos produced from
the work of C.P. Lutz,
Zeppenfeld, and D.M.
Eigler. Reprinted with
permission from
International Business
Machines
Corporation,
copyright 1995.
Iron atoms
arranged on a
copper (111)
surface. These
Kanji characters
represent the word
“atom”.
SCANNING TUNNELING
MICROSCOPY

44. 22
• Demonstrates "polymorphism"
The same atoms can
have more than one
crystal structure.
DEMO: HEATING AND
COOLING OF AN IRON WIRE
Temperature, C
BCC Stable
FCC Stable
914
1391
1536
shorter
longer!
shorter!
longer
Tc768 magnet falls off
BCC Stable
Liquid
heat up
cool down

45. • Atoms may assemble into crystalline or
amorphous structures.
• We can predict the density of a material,
provided we know the atomic weight, atomic
radius, and crystal geometry (e.g., FCC,
BCC, HCP).
• Material properties generally vary with single
crystal orientation (i.e., they are anisotropic),
but properties are generally non-directional
(i.e., they are isotropic) in polycrystals with
randomly oriented grains.
23
SUMMARY