Estrutura Atômicas e Ligações

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ATOMIC STRUCTURE AND 
INTERATOMIC BONDING
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Why study Atomic structure and 
interatomic bonding?
• The type of bond allows us to explain a 
material’s properties.
• -ex: Carbon,
• Graphite (soft and has “greasy” feel to it)
• Diamond ( the hardest known material)
• The dramatic disparity in properties is 
directly attributable to a type of 
interatomic bonding found in graphite that 
doesn’t exist in diamond.
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Atomic Structure
• Atom consist of a very small 
nucleus composed of protons and 
neutrons, which encircled by 
moving electrons
–Electrons (electrically charged, 
negative in sign)
–Protons (electrically charge, 
positive in sign)
–Neutrons (electrically neutral)
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Electron Configuration
• Valence electrons are those that occupy the 
outermost filled shell.
– The physical and mechanical properties of solids 
are based on valence electrons
– Stable electron configuration ( the outermost or 
valence electron shell is completely filled)
• -ex: inert gases (neon, argon helium)
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• have discrete energy states
• tend to occupy lowest available energy state.
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...
Electron Energy States
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• have complete s and p subshells
• tend to be unreactive.
Stable electron configurations...
Z Element Configuration 
2 He 1s2 
10 Ne 1s22s22p6 
18 Ar 1s22s22p63s23p6 
36 Kr 1s22s22p63s23p63d104s24p6
Stable Electron Configurations
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
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• 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 
The Periodic Table
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• 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.
Electronegativity
• Having a tendency to accept valence electrons
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Atomic Bonding
• Primary Bonding
–Ionic
–Covalent
–Metallic
• Secondary Bonding
–Van Der Waals 
–Hydrogen
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Na (metal) 
unstable 
Cl (nonmetal) 
unstable 
electron 
+ - 
Coulombic 
Attraction 
Na (cation) 
stable 
Cl (anion) 
stable 
• Occurs between + and - ions.
• Requires electron transfer.
• Large difference in electronegativity required.
• Example: NaCl
Ionic Bonding
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• 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
Examples: Ionic Bonding
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• 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
Covalent Bonding
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• Molecules with nonmetals
• Molecules with metals and nonmetals
• Elemental solids (RHS of Periodic Table)
• 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
Examples: Covalent Bonding
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• Arises from a sea of donated valence electrons
(1, 2, or 3 from each atom).
• Primary bond for metals and their alloys
+ + +
+ + +
+ + +
Metallic Bonding
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Secondary bonds
• Van der Waals
– no electrons are transferred
– attraction depends on distribution of positive and 
negative charge within each atom i.e. dipole
– Temporary or Permanent dipoles
• Hydrogen bonding
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Arises from interaction between dipoles
• Permanent dipoles-molecule induced
• Fluctuating dipoles
+ - secondary bonding + -
H Cl H Clsecondary bonding
secondary bonding
HH HH
H2 H2
secondary 
bonding
ex: liquid H2asymmetric electron clouds
+ - + -
secondary 
bonding
-general case:
-ex: liquid HCl
-ex: polymer
Secondary Bonding
• Dipoles: a pair of equal yet opposite electrical 
charges that are separated by a small distance
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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
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Ceramics
(Ionic & covalent bonding):
Metals
(Metallic bonding):
Polymers
(Covalent & Secondary):
secondary bonding
Large bond energy
large Tm
large E
small a
Variable bond energy
moderate Tm
moderate E
moderate a
Directional Properties
Secondary bonding dominates
small T
small E
large a
Summary: Properties from bonding
(Melting temperature, Elastic Modulus, Coefficient of thermal expansion)