材料科学基础
Fundamental of Materials
Prof,Tian Min Bo
Tel,62795426, 62772851
E-mail,tmb@mail.tsinghua.edu.cn
Department of Material Science and Engineering
Tsinghua University,Beijing 100084
Lesson two
§ 1.2 Atomic bonding
?Ⅰ.Bonding forces and energies
FN, net force
FA, attractive force
FR, repulsive force
RAN FFF ??
?? F drE
For atomic systems:
RAN EEE ??
Bonding energies:
? Ⅱ.Primary interatomic bonds
1,Ionic bonding
Ionic bonding is always found in compounds that are
composed of both metallic and nonmetallic elements,
elements that are situated at the horizontal extremities of
the periodic table.
2
0
2
21
a t t r a c t iv e 4 a
eZZF
??
?? 1r e p u l s iv e ??? n
a
nbF
12
0
2
21
n e t 4 ????? na
nb
a
eZZF
??
Interionic Forces
Z1,Z2＝ number of electrons removed or added from the
atoms during the ion formation
e ＝ electron charge
a ＝ interionic separation distance
ε0＝ permittivity of free space＝ 8.85× 10-12C2/(N·m2)
Interionic Energies
na
b
a
eZZE ???
0
2
21
n e t 4 ??
Attractive
energy
Repulsive
energy
Example problem 2.1
If the attractive force between a pair of Mg2+and S2- is
1.49× 10-8N and if the S2- ion has a radius of 0.184nm,calculate a
value for the ionic radius of the Mg2+ ion in nanometers.
Solution
2
0
2
21a t t r a c t iv e
4 a
eZZF
?????
nm249.0
)N1049.1](mN(C1085.8[4
)C1060.1)(2)(2(
4 82212
219
a t t r a c t iv e0
2
21
0
?
???
???
?
?
?? ??
?
）??? F
eZZ
a
nm065.00, 1 8 4 n mnm249.022
22
0Mg
Mg0
??????
??
??
??
S
S
rar
rra?又
2,Covalent bonding
Materials with covalent bonding are
characterized by bonds that are formed by
sharing of valence electrons among two or more
atoms.
3,Metallic bonding
Metallic bonding occurs in solid metals,
In metals in solid state,atoms are packed relatively close
together in a systematic pattern or crystal structure.
? Ⅲ.Secondary bonding
（ Van Der waals bonding)
The driving force for secondary bonding is the attraction
of the electric dipoles contained in atoms or molecules.
An electric dipole moment is created when two equal and
opposite charges are separated.
??
Neutral atom E
Van Der waals bonding
A dipole moment is defined as the charge value
multiplied by the separation distance between
positive and negative charges,or
qd??
m o m e n td ip o le??
c h a r g ee le c t r icofm a g n it u d e?q
c e n t e r sc h a r g et h eb e t w e e nd i s t a n c es e p a r a t i o n?d
London forces
If the interactions are between two dipoles that are induced
in atoms or molecules,we refer to them as London forces.
?? ??
1,Van der waals interactions
H
H
? oxygen??
?
?
Debye forces
When an induced dipole interacts with a molecule that has
a permanent dipole moment,we refer to this interaction as a
Debye interaction.
H
H
H
H
??oxygen oxygen
?
?
?
?
Keesom forces
If the interactions are between molecules that are
permanently polarized,we refer to these as Keesom
interaction.
2,Secondary bonding
Fluctuating Dipole bonds
These bonding forces arise because the asymmetrical
distribution of electron charge distribution in these atoms
creates electric dipoles,
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?
? ?
??
??
?? ?
?
??
?
?
? ??
?
?
? ?
?
?
?
?
?
?? ?
?
?
?
?
? ?
?
?
??
Permanent Dipole bonds
Permanent Dipole bonds exist between adjacent polar
molecules,
?105
??
??
??
??
??
??
??
??
??
??
??
??
bon ding
Hydrogen
3,Mixed bonding
? Ionic-Covalent Mixed bonding
? Metallic-Covalent Mixed Bonding
? Metallic-Ionic Mixed Bonding
%)100)(1(c h a r a c t e ri o n i c% 2BA ))(4/1( XXe ????
XA and XB are the electronegativities of the atoms A
and B in the compound
Summary
Ionic bonding
Primary atomic bonds Covalent bonding
Metallic bonding
Permanent dipole bonds
Secondary atomic bonds
Fluctuating dipole bonds
Examples and Discussions
Exercise
Thank you !
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