CHAPTER 2:
Atomic Structure and Interatomic
Bonding
ISSUES TO ADDRESS...
• What promotes bonding?
• What types of bonds are there?
• What properties are inferred from bonding?
Chapter 2- 1
BOHR ATOM
orbital electrons:
n = principal
quantum number
1
2
n=3
Adapted from Fig. 2.1,
Callister 6e.
Nucleus: Z = # protons
= 1 for hydrogen to 94 for plutonium
N = # neutrons
Atomic mass A ≈ Z + N
Chapter 2- 2
ELECTRON ENERGY STATES
Electrons...
• have discrete energy states
• tend to occupy lowest available energy state.
Adapted from Fig. 2.5,
Callister 6e.
Chapter 2- 3
STABLE ELECTRON CONFIGURATIONS
Stable electron configurations...
• have complete s and p subshells
• tend to be unreactive.
Adapted from Table 2.2,
Callister 6e.
Chapter 2- 4
SURVEY OF ELEMENTS
• Most elements: Electron configuration not stable.
Electron configuration
1s1
1s2
(stable)
1s22s1
1s22s2
Adapted from Table 2.2,
1s22s22p 1
Callister 6e.
1s22s22p 2
...
1s22s22p 6
(stable)
1s22s22p 63s1
1s22s22p 63s2
1s22s22p 63s23p 1
...
1s22s22p 63s23p 6
(stable)
...
1s22s22p 63s23p 63d 10 4s246
(stable)
• Why? Valence (outer) shell usually not filled completely.
Chapter 2- 5
THE PERIODIC TABLE
• Columns: Similar Valence Structure
Adapted
from Fig. 2.6,
Callister 6e.
Electropositive elements:
Readily give up electrons
to become + ions.
Electronegative elements:
Readily acquire electrons
to become - ions.
Chapter 2- 6
ELECTRONEGATIVITY
• Ranges from 0.7 to 4.0,
• Large values: tendency to acquire electrons.
Smaller electronegativity
Larger electronegativity
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.
Chapter 2- 7
IONIC BONDING
•
•
•
•
Occurs between + and - ions.
Requires electron transfer.
Large difference in electronegativity required.
Example: NaCl
Chapter 2- 8
EXAMPLES: IONIC BONDING
• Predominant bonding in Ceramics
NaCl
MgO
CaF2
CsCl
H
2.1
Li
1.0
Be
1.5
Na
0.9
Mg
1.2
K
0.8
Ca
1.0
Sr
1.0
Rb
0.8
Cs
0.7
Fr
0.7
Ti
1.5
Cr
1.6
Ba
0.9
Fe
1.8
Ni
1.8
He
O
3.5
Zn
1.8
As
2.0
F
4.0
Cl
3.0
Ne
-
Br
2.8
I
2.5
Kr
Xe
Rn
-
At
2.2
Ar
-
Ra
0.9
Give up electrons
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.
Chapter 2- 9
COVALENT BONDING
• Requires shared electrons
• Example: CH4
C: has 4 valence e,
needs 4 more
H: has 1 valence e,
needs 1 more
Electronegativities
are comparable.
Adapted from Fig. 2.10, Callister 6e.
Chapter 2- 10
EXAMPLES: COVALENT BONDING
H2
H
2.1
Li
1.0
Na
0.9
K
0.8
Rb
0.8
Cs
0.7
Sr
1.0
Ba
0.9
Fr
0.7
Ra
0.9
•
•
•
•
C(diamond)
SiC
Be
1.5
Mg
1.2
Ca
1.0
column IVA
H2O
Ti
1.5
Cr
1.6
Fe
1.8
F2
He
O
2.0
C
2.5
Ni
1.8
Zn
1.8
Ga
1.6
Si
1.8
Ge
1.8
As
2.0
Sn
1.8
Pb
1.8
F
4.0
Cl
3.0
Ne
-
Br
2.8
Ar
Kr
-
I
2.5
Xe
-
At
2.2
Rn
-
Cl2
GaAs
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.
Molecules with nonmetals
Molecules with metals and nonmetals
Elemental solids (RHS of Periodic Table)
Compound solids (about column IVA)
Chapter 2- 11
METALLIC BONDING
• Arises from a sea of donated valence electrons
(1, 2, or 3 from each atom).
Adapted from Fig. 2.11, Callister 6e.
• Primary bond for metals and their alloys
Chapter 2- 12
SECONDARY BONDING
Arises from interaction between dipoles
• Fluctuating dipoles
Adapted from Fig. 2.13, Callister 6e.
• Permanent dipoles-molecule induced
-general case:
-ex: liquid HCl
Adapted from Fig. 2.14,
Callister 6e.
Adapted from Fig. 2.14,
Callister 6e.
-ex: polymer
Chapter 2- 13
SUMMARY: BONDING
Type
Bond Energy
Comments
Ionic
Large!
Nondirectional (ceramics)
Covalent
Variable
Directional
large-Diamond semiconductors, ceramics
small-Bismuth
polymer chains)
Metallic
Variable
large-Tungsten
small-Mercury
Nondirectional (metals)
smallest
Directional
inter-chain (polymer)
inter-molecular
Secondary
Chapter 2- 14
PROPERTIES FROM BONDING: TM
• Bond length, r
F
• Melting Temperature, Tm
F
r
• Bond energy, Eo
Tm is larger if Eo is larger.
Chapter 2- 15
PROPERTIES FROM BONDING: E
• Elastic modulus, E
Elastic modulus
F
L
=E
Ao
Lo
• E ~ curvature at ro
Energy
unstretched length
ro
r
E is larger if Eo is larger.
smaller Elastic Modulus
larger Elastic Modulus
Chapter 2- 16
PROPERTIES FROM BONDING: a
• Coefficient of thermal expansion, a
coeff. thermal expansion
L
= a(T2-T1)
Lo
• a ~ symmetry at ro
a is larger if Eo is smaller.
Chapter 2- 17
SUMMARY: PRIMARY BONDS
Ceramics
(Ionic & covalent bonding):
Metals
(Metallic bonding):
Polymers
(Covalent & Secondary):
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
Chapter 2- 18
ANNOUNCEMENTS
Reading:
Core Problems:
Self-help Problems:
Chapter 2- 0