Lecture 2 Bonding and Properties
Transcript of Lecture 2 Bonding and Properties
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ISSUES TO ADDRESS...
What promotes bonding?
What types of bonds are there?
What properties are formed from bonding?
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BONDING AND PROPERTIES
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Nucleus: Z = # protons
2
orbital electrons:
n = principalquantum number
n=3 21
= 1 for hydrogen to 94 for plutoniumN = # neutrons
Atomic mass A Z + N
Adapted from Fig. 2.1,
Callister 6e.
BOHR ATOM
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have discrete energy states tend to occupy lowest available energy state.
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Electrons...
ELECTRON ENERGY STATES
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have complete s and p subshells
tend to be unreactive.
Stable electron configurations...
Adapted from Table 2.2,
Callister 6e.
STABLE ELECTRON CONFIGURATIONS
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Why? Valence(outer) shell usually not filled completely.
Most elements: Electron configuration not stable.
Electron configuration1s1
1s2 (stable)1s22s11s22s21s22s22p 1
1s2
2s2
2p2
...
1s22s22p 6 (stable)1s22s22p 63s11s22s22p 63s21s22s22p 63s23p 1...
1s22s22p 63s23p 6 (stable)...
1s22s22p 63s23p 63d 104s246 (stable)
Adapted from Table 2.2,
Callister 6e.
SURVEY OF ELEMENTS
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Columns: Similar ValenceStructure
Electropositive elements:
Readily give up electronsto become + ions.
Electronegative elements:
Readily acquire electronsto become - ions.
Adapted from
Fig. 2.6,
Callister 6e.
THE PERIODIC TABLE
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Ranges from 0.7to 4.0,
Smaller electronegativity Larger electronegativity
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
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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-
F4.0
Cl3.0
Br2.8
I2.5
At2.2
Li1.0
Na0.9
K0.8
Rb0.8
Cs0.7
Fr0.7
H2.1
Be1.5
Mg1.2
Ca1.0
Sr1.0
Ba0.9
Ra0.9
Ti1.5
Cr1.6
Fe1.8
Ni1.8
Zn1.8
As2.0
CsCl
MgO
CaF2
NaCl
O3.5
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
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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.
Adapted from Fig. 2.10, Callister 6e.
COVALENT BONDING
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Molecules with nonmetals
Molecules with metals andnonmetals
Elemental solids (RHS of Periodic Table)
Compound solids (about column IVA)
He-
Ne-
Ar-
Kr-
Xe-
Rn-
F4.0
Cl3.0
Br2.8
I2.5
At2.2
Li1.0
Na0.9
K0.8
Rb0.8
Cs0.7
Fr0.7
H2.1
Be1.5
Mg1.2
Ca1.0
Sr1.0
Ba0.9
Ra0.9
Ti1.5
Cr1.6
Fe1.8
Ni1.8
Zn1.8
As2.0
SiC
C(diamond)
H2O
C2.5
H2
Cl2
F2
Si1.8
Ga1.6
GaAs
Ge1.8
O2.0
column
IVA
Sn1.8
Pb1.8
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 and1940, 3rd edition. Copyright 1960 by Cornell University.
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 theiralloys
Adapted from Fig. 2.11, Callister 6e.
METALLIC BONDING
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Arises from interaction between dipoles
Permanent dipoles-molecule induced
Fluctuating dipoles
-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
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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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Bond length, r
Bond energy, Eo
FF
r
Melting Temperature, Tm
Tmis larger if Eois larger.
PROPERTIES FROM BONDING: TM
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Elastic modulus, E
E ~ curvature at ro
LF
Ao= E
Lo
Elastic modulus
r
larger Elastic Modulus
smaller Elastic Modulus
Energy
rounstretched length
E is larger if Eois larger.
PROPERTIES FROM BONDING: E
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Coefficient of thermal expansion, a
a~ symmetry at ro
ais larger if Eois smaller.
= a (T2-T1)L
Lo
coeff. thermal expansion
PROPERTIES FROM BONDING: a
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Ceramics
(Ionic & covalent bonding):
Metals
(Metallic bonding):
Polymers
(Covalent & Secondary):
Large bond energy
large Tm
large Esmall a
Variable bond energy
moderate Tm
moderate Emoderate a
Directional Properties
Secondary bonding dominates
small Tsmall Elarge a
SUMMARY: PRIMARY BONDS