ch02 - atomic bonding
TRANSCRIPT
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P A R TO N E
CHAPTER 2Atomic Bonding
The scanning tunneling microscope (Section
4.7) allows the imaging of individual atoms
bonded to a material surface. In this case, the
microscope was also used to manipulate the
atoms into a simple pattern. Four lead atoms
are shown forming a rectangle on the surface
of a coppercrystal. (FromG. Meyer andK. H.
Rieder, MRS Bulletin 23 28 [1998].)
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Outer orbital(with foursp3hybrid
bonding electrons)
Nucleus (withsix protons andsix neutrons)
Inner orbital(with two 1selectrons)
Figure 2-1 Schematic of the planetary model of a12C atom.
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1
H1.008
3Li
6.941
4Be
9.012
I A
II A III A IV A V
VIII
III B IV B V B VI B VII B I B
11Na
22.99
12Mg
24.31
13Al
26.98
14Si
28.09
1P
30
5B
10.81
6C
12.01
7N
14
19K
39.10
20Ca
40.08
21Sc
44.96
22Ti
47.90
23V
50.94
24Cr
52.00
25Mn
54.94
26Fe
55.85
27Co
58.93
28Ni
58.71
29Cu
63.55
30Zn
65.38
31Ga
69.72
32Ge
72.59
3A
74
37Rb85.47
38Sr87.62
39Y88.91
40Zr91.22
41Nb92.91
42Mo95.94
43Tc98.91
44Ru101.07
45Rh102.91
46Pd106.4
47Ag107.87
48Cd112.4
49In114.82
50Sn118.69
5S121
55Cs
132.91
56Ba
137.33
57La
138.91
87Fr
(223)
88Ra
226.03
89Ac
(227)
72Hf
178.49
73Ta
180.95
74W
183.85
75Re
186.2
76Os
190.2
77Ir
192.22
78Pt
195.09
79Au
196.97
80Hg
200.59
81Tl
204.37
82Pb
207.2
8B
208
58Ce
140.12
59Pr
140.91
60Nd
144.24
61Pm
(145)
62Sm
150.4
63Eu
151.96
64Gd
157.25
65Tb
158.93
66Dy
162.50
67Ho
164.93
68Er
167.26
69Tm
168.93
7Y
17390Th
232.04
91Pa
231.04
92U
238.03
93Np
237.05
94Pu
(244)
95Am
(243)
96Cm
(247)
97Bk
(247)
98Cf
(251)
99Es
(254)
100Fm
(257)
101Md
(258)
10N
(25
II B
Figure 2-2 Periodic table of the elements indicating atomic number and atomic mas
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Energy (eV)
283.9
6.5 2 (sp3)
1s
0
Figure 2-3 Energy-level diagram for the orbital electrons in a12C atom.Notice the sign convention. An attractive energy is negative. The 1s elec-
trons are closer to the nucleus (see Figure 21) and more strongly bound(binding energy = 283.9 eV). The outer orbital electrons have a bind-ing energy of only 6.5 eV. The zero level of binding energy correspondsto an electron completely removed from the attractive potential of thenucleus.
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Electron transfer
Ionic bond
Na Cl
Na+ Cl
Figure 2-4 Ionic bonding between sodium
and chlorine atoms. Electron transfer fromNa to Cl creates a cation (Na+) and ananion (Cl). The ionic bond is due to thecoulombic attraction between the ions ofopposite charge.
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Cl
Na+
Figure 2-5 Regular stacking of Na+
and Cl ions in solid NaCl. Thisis indicative of the nondirectionalnature of ionic bonding.
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0.70.60.50.40.3a(nm)
Na+ Cl
0.20.1
a
4
3
2
1
00
Fc
1
09(N)
Figure 2-6 Plot of the coulombic force (Equation 2.1) for a Na+Cl pair.
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0.7a(nm)
0.60.50.40.3
Na+
Fc(coulombic force of attraction)
FR(repulsive force)
F(net bonding force)
Cl
0.20.1
a0
4
3
2
1
1
2
3
4
0
Fc1
09(N)
Figure 2-7 Net bonding force curve for a Na+Cl pair showing an equi-librium bond length ofa0 = 0.28nm.
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+
0
Bondingforce
Na+ Cl
a
+
0
a0
Bondingenergy
a
Figure 2-8 Comparison of the bonding force curveand the bonding energy curve for a Na+Cl
pair. SinceF = dE/da, the equilibrium bondlength (a0) occurs whereF = 0and E is a mini-mum (see Equation 2.5).
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(a)
(b)
(c)
a0
rClrNa+
Figure 2-9 Comparison of (a) a plane-tary model of a Na+Cl pair with(b) a hard-sphere model and (c) a
soft-sphere model.
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Na
Na+
Cl
Cl
Figure 2-10 Formation of an ionic bond between sodium and chlorine inwhich the effect of ionization on atomic radius is illustrated. The cation(Na+) becomes smaller than the neutral atom (Na), while the anion(Cl) becomes larger than the neutral atom (Cl).
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R= 1.0
r= 0.2
CN = 1 possible CN = 2 possible CN = 3 maximum
Figure 2-11 The largest number of ions of radiusR that can coordinate an atom of raddius ratio,r/R = 0.2. (Note: The instability for CN = 4can be reduced butnotelthree-dimensional, rather than a coplanar, stacking of the larger ions.)
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30
cos 30 = 0.866 = = 0.155R
r + R
r
R
Figure 2-12 The minimum radius ratio, r/R,that can produce threefold coordinationis 0.155.
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(a)
(b)
(d)
(c)
Cl Cl
Cl Cl
Figure 2-13 The covalent bond ina molecule of chlorine gas, Cl
2,
is illustrated with (a) a plane-tary model compared with (b)the actual electron density and(c) an electron-dot schematicand (d) a bond-line schematic.
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C C
HH
C C C C C
HH
H H
H H
H
H
H
H
H
H
C C C
H
H
H
H
H
H
(a)
(b)
Ethylenemolecule
Ethylenemer
Polyethylenemolecule
.. . .. . . .
. . . .. . . .
Figure 2-14 (a) An ethylene molecule (C2H4) is comparedwith (b) a polyethylene molecule ( C2H4) nthat re-
sults from the conversion of the C=C double bond intotwo CC single bonds.
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C
H
H
C
H
H
C
H
H
CH H
CH
HC
H
H
C
H
H
C
H
H
C
H
HC
H
HC H
H
C HH
C
H
H
C
H
H
C
H
H C
H
H
C
H
H
C
H
H
C
H
HC
H
HC
H
H
C
H
H
CH
H
CH
H
CH H
CH H
CH H
CH H
CH H
CH H
CH H
CH
HCH
HC
H
H
CH
H
C
H
H
C
H
HC
H
HC
H
H
C
H
HC
H
H
CH
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
CH H
C
H
H
CH
H
CH
CH
H
CH
H
CH
C
H
H
C
H
H
C
H
H.
.
.
.
.
.
.
.
. .. .
....
....
....
Figure 2-15 Two-dimensional schematic representation of the spaghettilike solid polyethylene.
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C
C C
C C
CC
C
C
CC
C
C
C
C
C
Figure 2-16 Three-dimensional structure of bond-ing in the covalent solid, carbon (diamond).Each carbon atom (C) has four covalent bonds
to four other carbon atoms. (This geometry canbe compared with the diamond cubic struc-ture of Figure 323.) In this illustration, the bond-line schematic of covalent bonding is givena perspective view to emphasize the spatial ar-rangement of bonded carbon atoms.
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O2
Si4+
Figure 2-17 The SiO44 tetrahedronrepresented as a cluster of ions. In
fact, the SiO bond exhibits bothionic and covalent character.
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Bond energy
0
+
E a
Bond length
Figure 2-18 The general shape of the bond energy curve as well asassociated terminology applies to covalent as well as ionic bond-ing. (The same is true of metallic and secondary bonding.)
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109.5
C
Figure 2-19 Tetrahedral configuration of covalentbonds with carbon. The bond angle is 109.5.
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C C
ClH
H H
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C C C C C
HCl
H H
Cl
H
H
H
C C
Cl
H
H
H
Cl
H
C C C
H
H
Cl
H
H
H
mer
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CC CC
CC C C
54.75
l109.5
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Cu2+ion core(cutaway view)
Electron cloud from valence electrons
Figure 2-20 Metallic bond consisting of an electron cloud, or gas. An imaginaryslice is shown through the front face of the crystal structure of copper, reveal-
ing Cu2+ ion cores bonded by the delocalized valence electrons.
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1H2.1
3Li1.0
4Be1.5
I A
II A III A IV A V
VIII
III B IV B V B VI B VII B I B
11Na0.9
12Mg1.2
13Al1.5
14Si1.8
5B
2.0
6C
2.5
19
K0.8
20
Ca1.0
21
Sc1.3
22
Ti1.5
23
V1.6
24
Cr1.6
25
Mn1.5
26
Fe1.8
27
Co1.8
28
Ni1.8
29
Cu1.9
30
Zn1.6
31
Ga1.6
32
Ge1.8
37Rb0.8
38Sr1.0
39Y1.2
40Zr1.4
41Nb1.6
42Mo1.8
43Tc1.9
44Ru2.2
45Rh2.2
46Pd2.2
47Ag1.9
48Cd1.7
49In1.7
50Sn1.8
55Cs0.7
56Ba0.9
57-71La-Lu1.1-1.2
87Fr0.7
88Ra0.9
89-102Ac-No1.1-1.7
72Hf1.3
73Ta1.5
74W1.7
75Re1.9
76Os2.2
77Ir2.2
78Pt2.2
79Au2.4
80Hg1.9
81Tl1.8
82Pb1.8
II B
Figure 2-21 The electronegativities of the elements. (After Linus Pauling, The Natureand the Structure of Molecules and Crystals; An Introduction to Modern StructuraCornell University Press, Ithaca, New York, 1960)
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+
Magnitude ofdipole moment
Secondarybond
Isolated Ar atom
+
Center of negative(electron) charge
Cecha
Figure 2-22 Development of induced dipoles in adjacent argon atoms leading to a weak, sgree of charge distortion shown here is greatly exaggerated.
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Dipole
HH
O
+
=
+
Figure 2-23 Hydrogen bridge. This secondary bond is formedbetween two permanent dipoles in adjacent water molecules.(From W. G. Moffatt, G. W. Pearsall, and J. Wulff,TheStructure and Properties of Materials,Vol. 1: Structures,
John Wiley & Sons, Inc., New York, 1964.)
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covalent
Semiconductors
Polymers
metallic secondary
Ceramics and glassMetals
ionic
Figure 2-24 Tetrahedron representing the relative contri-bution of different bond types to the four fundamentalcategories of engineering materials (the three structuraltypes plus semiconductors).
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a0
Referenceion
+ + + + +
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C C
H
C
H
nn
H H
C
CH3 H
C C
H
C
H
H H
C
CH3 H
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nnOC
H
H
CC
H
H
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C C
FF
F F
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C C
HF
F H
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C C
F
F F
C FF
F
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Na (solid) + Cl2(g)
NaCl (solid) Na+ (g) + Cl (g)
Na (g) + Cl (g)1
2
Hf