Ch1 And Ch 2
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Introduction
MAE 2321
Classification of Materials • Metals: Metallic elements, large numbers of nonlocalized electrons, Quite strong, yet deformable, Good conductors of electricity. • Ceramics: Compounds between metallic and nonmetallic elements, such as oxides, nitrides, and carbides. Hard but very brittle, Insulators of electricity • Polymers: Organic compounds; very large molecular structures. Usually not for high temperature applications. (eg: plastics, rubbers) • Semiconductors: Elements in between metallic and non metallic elements (see periodic table) or their compounds. The electrical properties are extremely sensitive to the presence of minute concentrations of impurity atoms, which can be controlled over very small spatial regions. • Composites: Consist of more than one materials type. Better combination of properties.
MAE 2321
Properties of Materials
• Mechanical properties: applied load or force • Electrical properties: electric field • Thermal properties: temperature change • Magnetic properties: magnetic field • Optical properties: electromagnetic/light radiation • Deteriorative properties: chemical reactivity
MAE 2321
Chapter 2 Atomic Structure and Interatomic Bonding
MAE 2321
Why study atomic structure and interatomic bonding? • Atomic arrangement determines the material properties (mechanical, electrical, thermal, optical, magnetic) • Example: Carbon (C) • Diamond • Graphite • Carbon Nanotube • C60 (Buckyball)
MAE 2321
Carbon Nanotube
MAE 2321
C60
MAE 2321
Fundamental Concepts • Atom: Composed of proton, neutron, electron • Atomic Number (Z): The number of protons in the nucleus ex: H(Z=1), U(Z=92) • Atomic Mass (A): The mass of an atom • Atomic Mass Unit (amu): •A≈Z+N • Isotopes: the same Z, but different N Ex: 1H (hydrogen): A ≈ 1+ 0 = 1 2H (deuterium): A ≈ 1+ 1 = 2 MAE 2321
Fundamental Concepts (cont.) • Atom Weight: The weighted average of the atomic masses of the atom’s naturally occurring isotopes. Ex: The atomic weight of iron is 55.85 amu (55.86g/mol)
MAE 2321
Review of Quantum Mechanics What is Quantum Mechanics? A systematic description of physical phenomena in the atomic scale (can be extended to the macro scale)
MAE 2321
The job of Quantum mechanics is to find a rule for the phenomena occurring in the atomic world
Analogy
MAE 2321
Quantum Mechanics • Bohr atomic model: Earlier Quantum Mechanics • Discrete orbitals (Fig. 2.1). • Energies of electrons are quantized (Fig. 2.2). • Wave-mechanical model: correct one • Electrons are no longer treated as a particle moving in a discrete orbital. • The probability to find an electron at a certain position is provided (Fig. 2.3).
MAE 2321
BOHR ATOMIC MODEL orbital electrons: n = principal quantum number 1 2 n=3
Nucleus • Discrete orbitals • Energies of electrons are quantized
MAE 2321
Energy Levels for Hydrogen
MAE 2321
Electron Distribution
Wave-mechanical Model Bohr Model
MAE 2321
Wave-mechanical model
MAE 2321
Electron Distributions in Noble-gas Atoms
MAE 2321
Quantum Numbers 1. Principal Quantum Number: n • n=1,2,3,4,5,--- (positive integers) • Shells: K, L, M, N, O, --• Related to the distance of an electron from the nucleus 2. Second Quantum Number (Orbital Angular Momentum Quantum Number): l 3. Third Quantum Number (Magnetic Quantum Number): m 4. Spin Quantum Number: ms MAE 2321
Electron Energy Levels
MAE 2321
MAE 2321
ELECTRON ENERGY STATES Electrons...
Increasing energy
• have discrete energy states • tend to occupy lowest available energy state.
4p
n=4
4s
n=3
3s
n=2 n=1
2s 1s
3d
3p 2p
MAE 2321
MAE 2321
STABLE ELECTRON CONFIGURATIONS Stable electron configurations... • have complete s and p subshells • tend to be unreactive. Z 2
Element Configuration He 1s2 10 Ne 1s22s 22p6 18 Ar 1s2 2s22p63s23p6 36 Kr 1s2 2s22p63s23p63d10 4s24p6
MAE 2321
Octet rule
Atoms tend to combine in such a way that each has eight electrons in its outermost shell, similar to the electron configuration of a noble gas.
MAE 2321
SURVEY OF ELEMENTS • Most elements: Electron configuration not stable. Element Atomic # Hydrogen 1 Helium 2 Lithium 3 Beryllium 4 Boron 5 Carbon 6 ... Neon 10 Sodium 11 Magnesium 12 Aluminum 13 ... Argon 18 ... ... Krypton 36
Electron configuration 1s 1 (stable) 1s 2 1s 22s 1 1s 22s 2 1s 22s 22p 1 1s 22s 22p 2 ... 1s 22s 22p 6 (stable) 1s 22s 22p 63s 1 1s 22s 22p 63s 2 1s 22s 22p 63s 23p 1 ... 1s 22s 22p 63s 23p 6 (stable) ... 1s 22s 22p 63s 23p 63d 10 4s 24 6 (stable)
• Why? Valence (outer) shell usually not filled completely. MAE 2321
give up 1e give up 2e give up 3e
Semiconductors
H
Li Be
Metal Nonmetal Intermediate
Na Mg
accept 2e accept 1e inert gases
Periodic Table
He
O
F
Ne
S
Cl
Ar
K Ca Sc
Se Br Kr
Rb Sr
Te
Y
Cs Ba Fr Ra
I
Xe
Po At Rn
Transition metals
MAE 2321
MAE 2321
ENERGY AND PACKING • Non dense, random packing
Energy typical neighbor bond length
typical neighbor bond energy
• Dense, regular packing
r
Energy typical neighbor bond length r
typical neighbor bond energy
Dense, regular-packed structures tend to have lower energy. MAE 2321
IONIC BONDING • • • •
Occurs between + and - ions. Requires electron transfer. Large difference in electronegativity required. Example: NaCl Na (metal) unstable
Cl (nonmetal) unstable electron
Na (cation) stable
+
Coulombic Attraction
Cl (anion) stable
MAE 2321
ELECTRONEGATIVITY • The power of attraction for the electrons • Ranges from 0.7 (Francium) to 4.0 (Fluorine) • Large values: tendency to acquire electrons H 2.1
He -
Li 1.0 Na 0.9
Be 1.5 Mg 1.2
K 0.8 Rb 0.8
Ca 1.0
Cs 0.7 Fr 0.7
Ba 0.9 Ra 0.9
F 4.0
Ti 1.5
Cr 1.6
Fe 1.8
Sr 1.0
Smaller electronegativity
Electropositive elements: Readily give up electrons to become + ions.
Ni 1.8
Zn 1.8
As 2.0
Cl 3.0 Br 2.8
Ne Ar Kr -
I 2.5 At 2.2
Xe Rn -
Larger electronegativity Electronegative elements: Readily acquire electrons to become - ions. MAE 2321
EXAMPLES: IONIC BONDING • Predominant bonding in Ceramics NaCl MgO H CaF2 2.1 Be Li CsCl 1.0 1.5 Na 0.9 K 0.8 Rb 0.8 Cs 0.7 Fr 0.7
O F 3.5 4.0 Cl 3.0
Mg 1.2 Ca 1.0 Sr 1.0
Ti 1.5
Cr 1.6
Ba 0.9
Fe 1.8
Ni 1.8
Zn 1.8
As 2.0
Br 2.8 I 2.5 At 2.2
He Ne Ar Kr Xe Rn -
Ra 0.9
Give up electrons
Acquire electrons MAE 2321
COVALENT BONDING • Requires shared electrons • Example: CH4 C: has 4 valence e, needs 4 more
CH4
H: has 1 valence e, needs 1 more
H
Electronegativities are comparable.
H
C
H
shared electrons from carbon atom H shared electrons from hydrogen atoms
Adapted from Fig. 2.10, Callister 6e.
MAE 2321
EXAMPLES: COVALENT BONDING H2 H 2.1 Li 1.0 Na 0.9 K 0.8
Be 1.5 Mg 1.2 Ca 1.0
Rb 0.8 Cs 0.7
Sr 1.0 Ba 0.9
Fr 0.7
Ra 0.9
column IVA
H2O C(diamond) SiC Ti 1.5
Cr 1.6
Fe 1.8
Ni 1.8
Zn 1.8
Ga 1.6
C 2.5 Si 1.8 Ge 1.8
F2 He O 2.0
As 2.0
Sn 1.8 Pb 1.8
F 4.0 Cl 3.0 Br 2.8 I 2.5 At 2.2
Cl2
Ne Ar Kr Xe Rn -
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) MAE 2321
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 MAE 2321
METALLIC CRYSTALS • tend to be densely packed. • have several reasons for dense packing: -Typically, only one element is present, so all atomic radii are the same. -Metallic bonding is not directional. -Nearest neighbor distances tend to be small in order to lower bond energy.
• have the simplest crystal structures.
MAE 2321
3
Secondary Bonding (Dipole Interactions)
MAE 2321
Hydrogen Bonding
MAE 2321
SECONDARY BONDING Arises from interaction between dipoles • Fluctuating dipoles ex: liquid H2 asymmetric electron H2 H2 clouds
+
- secondary + bonding
-
H H
Adapted from Fig. 2.13, Callister 6e.
H H
secondary bonding
• Permanent dipoles-molecule induced -general case: -ex: liquid HCl -ex: polymer
+
-
H Cl secon d
a ry b
secondary bonding secondary bonding
ondin
+
-
H Cl
Adapted from Fig. 2.14,
Callister 6e.
Adapted from Fig. 2.14,
Callister 6e.
g MAE 2321
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
MAE 2321
MAE 2321
MAE 2321
Classification of Materials • Metals: Metallic elements, large numbers of nonlocalized electrons, Quite strong, yet deformable, Good conductors of electricity. • Ceramics: Compounds between metallic and nonmetallic elements, such as oxides, nitrides, and carbides. Hard but very brittle, Insulators of electricity • Polymers: Organic compounds; very large molecular structures. Usually not for high temperature applications. (eg: plastics, rubbers) • Semiconductors: Elements in between metallic and non metallic elements (see periodic table) or their compounds. The electrical properties are extremely sensitive to the presence of minute concentrations of impurity atoms, which can be controlled over very small spatial regions. • Composites: Consist of more than one materials type. Better combination of properties.
MAE 2321
Properties of Materials
• Mechanical properties: applied load or force • Electrical properties: electric field • Thermal properties: temperature change • Magnetic properties: magnetic field • Optical properties: electromagnetic/light radiation • Deteriorative properties: chemical reactivity
MAE 2321
Chapter 2 Atomic Structure and Interatomic Bonding
MAE 2321
Why study atomic structure and interatomic bonding? • Atomic arrangement determines the material properties (mechanical, electrical, thermal, optical, magnetic) • Example: Carbon (C) • Diamond • Graphite • Carbon Nanotube • C60 (Buckyball)
MAE 2321
Carbon Nanotube
MAE 2321
C60
MAE 2321
Fundamental Concepts • Atom: Composed of proton, neutron, electron • Atomic Number (Z): The number of protons in the nucleus ex: H(Z=1), U(Z=92) • Atomic Mass (A): The mass of an atom • Atomic Mass Unit (amu): •A≈Z+N • Isotopes: the same Z, but different N Ex: 1H (hydrogen): A ≈ 1+ 0 = 1 2H (deuterium): A ≈ 1+ 1 = 2 MAE 2321
Fundamental Concepts (cont.) • Atom Weight: The weighted average of the atomic masses of the atom’s naturally occurring isotopes. Ex: The atomic weight of iron is 55.85 amu (55.86g/mol)
MAE 2321
Review of Quantum Mechanics What is Quantum Mechanics? A systematic description of physical phenomena in the atomic scale (can be extended to the macro scale)
MAE 2321
The job of Quantum mechanics is to find a rule for the phenomena occurring in the atomic world
Analogy
MAE 2321
Quantum Mechanics • Bohr atomic model: Earlier Quantum Mechanics • Discrete orbitals (Fig. 2.1). • Energies of electrons are quantized (Fig. 2.2). • Wave-mechanical model: correct one • Electrons are no longer treated as a particle moving in a discrete orbital. • The probability to find an electron at a certain position is provided (Fig. 2.3).
MAE 2321
BOHR ATOMIC MODEL orbital electrons: n = principal quantum number 1 2 n=3
Nucleus • Discrete orbitals • Energies of electrons are quantized
MAE 2321
Energy Levels for Hydrogen
MAE 2321
Electron Distribution
Wave-mechanical Model Bohr Model
MAE 2321
Wave-mechanical model
MAE 2321
Electron Distributions in Noble-gas Atoms
MAE 2321
Quantum Numbers 1. Principal Quantum Number: n • n=1,2,3,4,5,--- (positive integers) • Shells: K, L, M, N, O, --• Related to the distance of an electron from the nucleus 2. Second Quantum Number (Orbital Angular Momentum Quantum Number): l 3. Third Quantum Number (Magnetic Quantum Number): m 4. Spin Quantum Number: ms MAE 2321
Electron Energy Levels
MAE 2321
MAE 2321
ELECTRON ENERGY STATES Electrons...
Increasing energy
• have discrete energy states • tend to occupy lowest available energy state.
4p
n=4
4s
n=3
3s
n=2 n=1
2s 1s
3d
3p 2p
MAE 2321
MAE 2321
STABLE ELECTRON CONFIGURATIONS Stable electron configurations... • have complete s and p subshells • tend to be unreactive. Z 2
Element Configuration He 1s2 10 Ne 1s22s 22p6 18 Ar 1s2 2s22p63s23p6 36 Kr 1s2 2s22p63s23p63d10 4s24p6
MAE 2321
Octet rule
Atoms tend to combine in such a way that each has eight electrons in its outermost shell, similar to the electron configuration of a noble gas.
MAE 2321
SURVEY OF ELEMENTS • Most elements: Electron configuration not stable. Element Atomic # Hydrogen 1 Helium 2 Lithium 3 Beryllium 4 Boron 5 Carbon 6 ... Neon 10 Sodium 11 Magnesium 12 Aluminum 13 ... Argon 18 ... ... Krypton 36
Electron configuration 1s 1 (stable) 1s 2 1s 22s 1 1s 22s 2 1s 22s 22p 1 1s 22s 22p 2 ... 1s 22s 22p 6 (stable) 1s 22s 22p 63s 1 1s 22s 22p 63s 2 1s 22s 22p 63s 23p 1 ... 1s 22s 22p 63s 23p 6 (stable) ... 1s 22s 22p 63s 23p 63d 10 4s 24 6 (stable)
• Why? Valence (outer) shell usually not filled completely. MAE 2321
give up 1e give up 2e give up 3e
Semiconductors
H
Li Be
Metal Nonmetal Intermediate
Na Mg
accept 2e accept 1e inert gases
Periodic Table
He
O
F
Ne
S
Cl
Ar
K Ca Sc
Se Br Kr
Rb Sr
Te
Y
Cs Ba Fr Ra
I
Xe
Po At Rn
Transition metals
MAE 2321
MAE 2321
ENERGY AND PACKING • Non dense, random packing
Energy typical neighbor bond length
typical neighbor bond energy
• Dense, regular packing
r
Energy typical neighbor bond length r
typical neighbor bond energy
Dense, regular-packed structures tend to have lower energy. MAE 2321
IONIC BONDING • • • •
Occurs between + and - ions. Requires electron transfer. Large difference in electronegativity required. Example: NaCl Na (metal) unstable
Cl (nonmetal) unstable electron
Na (cation) stable
+
Coulombic Attraction
Cl (anion) stable
MAE 2321
ELECTRONEGATIVITY • The power of attraction for the electrons • Ranges from 0.7 (Francium) to 4.0 (Fluorine) • Large values: tendency to acquire electrons H 2.1
He -
Li 1.0 Na 0.9
Be 1.5 Mg 1.2
K 0.8 Rb 0.8
Ca 1.0
Cs 0.7 Fr 0.7
Ba 0.9 Ra 0.9
F 4.0
Ti 1.5
Cr 1.6
Fe 1.8
Sr 1.0
Smaller electronegativity
Electropositive elements: Readily give up electrons to become + ions.
Ni 1.8
Zn 1.8
As 2.0
Cl 3.0 Br 2.8
Ne Ar Kr -
I 2.5 At 2.2
Xe Rn -
Larger electronegativity Electronegative elements: Readily acquire electrons to become - ions. MAE 2321
EXAMPLES: IONIC BONDING • Predominant bonding in Ceramics NaCl MgO H CaF2 2.1 Be Li CsCl 1.0 1.5 Na 0.9 K 0.8 Rb 0.8 Cs 0.7 Fr 0.7
O F 3.5 4.0 Cl 3.0
Mg 1.2 Ca 1.0 Sr 1.0
Ti 1.5
Cr 1.6
Ba 0.9
Fe 1.8
Ni 1.8
Zn 1.8
As 2.0
Br 2.8 I 2.5 At 2.2
He Ne Ar Kr Xe Rn -
Ra 0.9
Give up electrons
Acquire electrons MAE 2321
COVALENT BONDING • Requires shared electrons • Example: CH4 C: has 4 valence e, needs 4 more
CH4
H: has 1 valence e, needs 1 more
H
Electronegativities are comparable.
H
C
H
shared electrons from carbon atom H shared electrons from hydrogen atoms
Adapted from Fig. 2.10, Callister 6e.
MAE 2321
EXAMPLES: COVALENT BONDING H2 H 2.1 Li 1.0 Na 0.9 K 0.8
Be 1.5 Mg 1.2 Ca 1.0
Rb 0.8 Cs 0.7
Sr 1.0 Ba 0.9
Fr 0.7
Ra 0.9
column IVA
H2O C(diamond) SiC Ti 1.5
Cr 1.6
Fe 1.8
Ni 1.8
Zn 1.8
Ga 1.6
C 2.5 Si 1.8 Ge 1.8
F2 He O 2.0
As 2.0
Sn 1.8 Pb 1.8
F 4.0 Cl 3.0 Br 2.8 I 2.5 At 2.2
Cl2
Ne Ar Kr Xe Rn -
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) MAE 2321
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 MAE 2321
METALLIC CRYSTALS • tend to be densely packed. • have several reasons for dense packing: -Typically, only one element is present, so all atomic radii are the same. -Metallic bonding is not directional. -Nearest neighbor distances tend to be small in order to lower bond energy.
• have the simplest crystal structures.
MAE 2321
3
Secondary Bonding (Dipole Interactions)
MAE 2321
Hydrogen Bonding
MAE 2321
SECONDARY BONDING Arises from interaction between dipoles • Fluctuating dipoles ex: liquid H2 asymmetric electron H2 H2 clouds
+
- secondary + bonding
-
H H
Adapted from Fig. 2.13, Callister 6e.
H H
secondary bonding
• Permanent dipoles-molecule induced -general case: -ex: liquid HCl -ex: polymer
+
-
H Cl secon d
a ry b
secondary bonding secondary bonding
ondin
+
-
H Cl
Adapted from Fig. 2.14,
Callister 6e.
Adapted from Fig. 2.14,
Callister 6e.
g MAE 2321
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
MAE 2321
MAE 2321
