Download - Chemistry 481(01) Spring 2014
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Chapter-2-1Chemistry 481, Spring 2017, LA Tech
Instructor: Dr. Upali Siriwardane
e-mail: [email protected]
Office: CTH 311 Phone 257-4941
Office Hours:
M,W 8:00-9:00 & 11:00-12:00 am;
Tu,Th, F 9:30 - 11:30 a.m.
April 4 , 2017: Test 1 (Chapters 1, 2, 3, 4)
April 27, 2017: Test 2 (Chapters (6 & 7)
May 16, 2016: Test 3 (Chapters. 19 & 20)
May 17, Make Up: Comprehensive covering all Chapters
Chemistry 481(01) Spring 2017
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Chapter-2-2Chemistry 481, Spring 2017, LA Tech
Molecular structure and bonding Lewis structures
2.1 The octet rule 2.2 Structure and bond properties 2.3 The VSEPR model
Valence-bond theory 2.4 The hydrogen molecule 2.5 Homonuclear diatomic molecules 2.6 Polyatomic molecules
Molecular orbital theory 2.7 An introduction to the theory 2.8 Homonuclear diatomic molecules 2.9 Heteronuclear diatomic2.10 Bond properties
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Chapter-2-3Chemistry 481, Spring 2017, LA Tech
What changes take place during this process of achieving closed shells?
a) sharing leads to covalent bonds and molecules Covalent Bond: each atom gives one electron
Coordinative bond: two electron comes from one atom
b) gain/loss of electrons lead to ionic bond Cations and anions: Electrostatic attractions
c) Sharing with many atoms lead to metallic bonds: delocalization of electrons
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Chapter-2-4Chemistry 481, Spring 2017, LA Tech
• Add all valence electrons and get valence electron pairs
• Pick the central atom: Largest atom normally or atom forming most bonds
• Connect central atom to terminal atoms
• Fill octet to all atoms (duet to hydrogen)
How do you get the Lewis Structure from Molecular formula?
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Chapter-2-5Chemistry 481, Spring 2017, LA Tech
1. Draw Lewis structure for SbF5, ClF3, and IF6+:
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Chapter-2-6Chemistry 481, Spring 2017, LA Tech
What is VSEPR TheoryValence Shell Electron Pair RepulsionThis theory assumes that the molecular structure is
determined by the lone pair and bond pair electron repulsion around the central atom
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Chapter-2-7Chemistry 481, Spring 2017, LA Tech
What Geometry is Possible around Central Atom?• What is Electronic or Basic Structure?• Arrangement of electron pairs around the central
atom is called the electronic or basic structure• What is Molecular Structure?• Arrangement of atoms around the central atom is
called the molecular structure
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Chapter-2-8Chemistry 481, Spring 2017, LA Tech
Possible Molecular Geometry
• Linear (180)• Trigonal Planar (120)• T-shape (90, 180)• Tetrahedral (109)• Square palnar ( 90, 180)• Sea-saw (90, 120, 180)• Trigonal bipyramid (90, 120, 180)• Octahedral (90, 180)
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Chapter-2-9Chemistry 481, Spring 2017, LA Tech
2. Predict geometry of central atom using VSEPR and the hybridization in problem 1.SbF5, ClF3, and IF6
+:
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Chapter-2-10Chemistry 481, Spring 2017, LA Tech
Formal ChargesFormal charge = valence electrons - assigned electronsIf there are two possible Lewis structures for a molecule, each has the same number of bonds, we can determine which is better by determining which has the least formal charge. It takes energy to get a separation of charge in the molecule •(as indicated by the formal charge) so the structure with the least formal charge should be lower in energy and thereby be the better Lewis structure
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Chapter-2-11Chemistry 481, Spring 2017, LA Tech
Formal Charge Calculation
Formal charge =
group number
in periodic table
number of
bonds
number of
unshared electrons
––
An arithmetic formula for calculating formal charge.
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Chapter-2-12Chemistry 481, Spring 2017, LA Tech
Electron counts" and formal charges in NH4
+ and BF4-
"
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Chapter-2-13Chemistry 481, Spring 2017, LA Tech
They both are!
O - S = O O = S - O
O S OThis results in an average of 1.5 bonds between
each S and O.Ave. Bond order= total pairs shared/ # bonds= 3/2=1.5
Resonance structures of SO2
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Chapter-2-14Chemistry 481, Spring 2017, LA Tech
Resonance structures of CO32- ion
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Chapter-2-15Chemistry 481, Spring 2017, LA Tech
Resonance structures of C6H6
• Benzene, C6H6, is another example of a compound for which resonance structure must be written.
• All of the bonds are the same length.
or
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Chapter-2-16Chemistry 481, Spring 2017, LA Tech
Exceptions to the octet rule
Not all compounds obey the octet rule.• Three types of exceptions• Species with more than eight electrons around
an atom.• Species with fewer than eight electrons around
an atom.• Species with an odd total number of electrons.
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Chapter-2-17Chemistry 481, Spring 2017, LA Tech
Valence-bond (VB) theory
VB theory combines the concepts of atomic orbitals,
hybrid orbitals, VSEPR, resonance structures, Lewis
structures and octet rule to describe the shapes and
structures of some common molecules.
It uses the overlap of atomic orbitals or hybrid orbitals of the
to from sigma (s) , pi (p) bonds and (d) bonds
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Chapter-2-18Chemistry 481, Spring 2017, LA Tech
Linear Combination of Atomic OrbitalsSymmetry Adapted
Linear Combination of Atomic Orbitals –LCAO
Atomic orbitals on single atom:
Hybridization
Atomic orbitals in a molecule with more than one atom:
Molecular Orbital (MO) formation
General rule
Number of Hybrid Orbital produced = # hybridized
Number of MO produced = # orbitals combined
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Chapter-2-19Chemistry 481, Spring 2017, LA Tech
What is hybridization?
Mixing of atomic orbitals on the central atom
Bonding
a hybrid orbital could over lap with another ()atomic orbital
or () hybrid orbital of another atom to make a covalent
bond.
possible hybridizations: sp, sp2, sp3, sp3d, sp3d2
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Chapter-2-20Chemistry 481, Spring 2017, LA Tech
How do you tell the hybridization of a central atom?
•Get the Lewis structure of the molecule
•Look at the number of electron pairs on the central atom. Note: double, triple bonds are counted as single electron pairs.
•Follow the following chart
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Chapter-2-21Chemistry 481, Spring 2017, LA Tech
Kinds of hybrid orbitalsHybrid geometry # of orbital sp linear 2sp2 trigonal planar 3sp3 tetrahedral 4sp3d trigonal bipyramid 5sp3d2 octahedral 6
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Chapter-2-22Chemistry 481, Spring 2017, LA Tech
What is hybridization?Mixing of atomic orbitals on the central atoms
valence shell (highest n orbitals)
Bonding: s p d
sp,
sp2,
sp3,
sp3d,
sp3d2
Px Py Pz dz2 dx
2- y
2
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Chapter-2-23Chemistry 481, Spring 2017, LA Tech
Possible hybridizations of s and p
sp-hybridization:
1 = 1/Ö2s - 1/Ö2p
2 = 1/Ö2s + 1/Ö2p
sp2
-hybridization:
1 = 1/Ö3s + 1/Ö6px + 1/Ö2py
2 = 1/Ö3s + 1/Ö6px - 1/Ö2py
3 = 1/Ö3s - 2/Ö6px
sp3
-hybridization:
1 = 1/Ö4s + 1/Ö4px + 1/Ö4py + 1/Ö4pz
2 = 1/Ö4s - 1/Ö4px - 1/Ö4py + 1/Ö4pz
3 = 1/Ö4s + 1/Ö4px - 1/Ö4py - 1/Ö4pz
4 = 1/Ö4s - 1/Ö4px + 1/Ö4py -1/Ö4pz
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Chapter-2-24Chemistry 481, Spring 2017, LA Tech
Possible hybridizations of s and p
sp-hybridization:
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Chapter-2-25Chemistry 481, Spring 2017, LA Tech
What are p and s bondss bondssingle bond resulting from head to head overlap of atomic orbital
p bonddouble and triple bond resulting from lateral or side way overlap of p atomic orbitals
d bonddouble and triple bond resulting from lateral or side way overlap of d atomic orbitals
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Chapter-2-26Chemistry 481, Spring 2017, LA Tech
Atoms with more than eight electrons• Except for species that contain hydrogen, this is
the most common type of exception.
• For elements in the third period and beyond, the d orbitals can become involved in bonding.
Examples
• 5 electron pairs around P in PF5
• 5 electron pairs around S in SF4
• 6 electron pairs around S in SF6
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Chapter-2-27Chemistry 481, Spring 2017, LA Tech
3. Why hypervalent compounds are formed by elements such as Si, P and S, but not by C,N and O?
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Chapter-2-28Chemistry 481, Spring 2017, LA Tech
An example: SO42-
1. Write a possible arrangement.
2. Total the electrons.6 from S, 4 x 6 from Oadd 2 for charge
total = 32
3. Spread the electronsaround.
S O
O
O
O
- - ||
||
S O
O
O
O
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Chapter-2-29Chemistry 481, Spring 2017, LA Tech
Atoms with fewer than eight electrons
Beryllium and boron will both form compounds where they have less than 8 electrons around them.
:Cl:Be:Cl: ::
::
:F:B:F:
:F:
::
::
::
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Chapter-2-30Chemistry 481, Spring 2017, LA Tech
Atoms with fewer than eight electrons
Electron deficient. Species other than hydrogen and helium that have fewer than 8 valence electrons.
They are typically very reactive species.F
|
B
|
F
F - +
H
|
:N – H
|
H
F H
| |
F - B <- N - H
| |
F H
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Chapter-2-31Chemistry 481, Spring 2017, LA Tech
What is a Polar Molecule?• Molecules with unbalanced electrical charges• Molecules with a dipole moment• Molecules without a dipole moment are called
non-polar molecules
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Chapter-2-32Chemistry 481, Spring 2017, LA Tech
How do you a Pick Polar Molecule?a) Get the molecular structure from VSEPR theoryb) From c (electronegativity) difference of bonds
see whether they are polar-covalent.c) If the molecule have polar-covalent bond, check
whether they cancel from a symmetric arrangement.
d) If not molecule is polar
Predicting symmetry of molecule and the polarity will be discussed in detail in Chapter 7.
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Chapter-2-33Chemistry 481, Spring 2017, LA Tech
Linear Combination of Atomic OrbitalsSymmetry Adapted
Linear Combination of Atomic Orbitals –LCAO
Atomic orbitals on single atom:
Hybridization
Atomic orbitals in a molecule with more than one atom:
Molecular Orbital (MO) formation
General rule
Number of Hybrid Orbital produced = # hybridized
Number of MO produced = # orbitals combined
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Chapter-2-34Chemistry 481, Spring 2017, LA Tech
6. Draw a diagram to illustrate each described overlap:
a) s bonding overlap of two p orbitals
b) d bonding overlap of two d orbitals
c) p bonding overlap of a p orbital and a d orbital
d) s antibonding overlap of a p and a d orbital
e) d antibonding overlap of two d orbitals.
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Chapter-2-35Chemistry 481, Spring 2017, LA Tech
What are p and s bondss bonds
p bond
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Chapter-2-36Chemistry 481, Spring 2017, LA Tech
What are d bonds
d bonddouble and triple bond resulting from lateral or side way overlap of d atomic orbitals
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Chapter-2-37Chemistry 481, Spring 2017, LA Tech
Kinds of hybrid orbitalsHybrid geometry # of orbital sp linear 2sp2 trigonal planar 3sp3 tetrahedral 4sp3d trigonal bipyramid 5sp3d2 octahedral 6
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Chapter-2-38Chemistry 481, Spring 2017, LA Tech
5. Using valence-bond (VB) theory to explain the bonding in the coordination complex ion, Co(NH3)6
3+.
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Chapter-2-39Chemistry 481, Spring 2017, LA Tech
Hybridization involving d orbitals•Co(NH3)6
3+ ion Co3+: [Ar] 3d6
•Co3+: [Ar] 3d6 4s0 4p0
•Concentrating the 3d electrons in the dxy, dxz, and
dyz orbitals in this subshell gives the following
electron configuration hybridization is sp3d2
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Chapter-2-40Chemistry 481, Spring 2017, LA Tech
5. What is the oxidation state of metal in (a) Co(NH3)6
3+ ion (b) PtCl42- ion.
a) [Co(NH3)6] 3+
Co3+ and NH3 is neutral
Oxidation Sate of Co3+ is +3 and NH3 is 0Therefore sum of the oxidation should be equal to +3 +3= Co(NH3)6 = (Co)3+6((NH3)0)= +3Co is +3 in [Co(NH3)6]3+ b) Pt is +2 in [PtCl4]2- because Cl- is -1
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Chapter-2-41Chemistry 481, Spring 2017, LA Tech
Linear Combination of Atomic OrbitalsSymmetry Adapted
Linear Combination of Atomic Orbitals –LCAO
Atomic orbitals on single atom:
Hybridization
Atomic orbitals in a molecule with more than one atom:
Molecular Orbital (MO) formation
General rule
Number of Hybrid Orbital produced = # hybridized
Number of MO produced = # orbitals combined
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Chapter-2-42Chemistry 481, Spring 2017, LA Tech
Basic Rules of Molecular Orbital TheoryThe MO Theory has five basic rules: • The number of molecular orbitals = the number of atomic
orbitals combined • Of the two MO's, one is a bonding orbital (lower energy)
and one is an anti-bonding orbital (higher energy) • Electrons enter the lowest orbital available • The maximum # of electrons in an orbital is 2 (Pauli
Exclusion Principle) • Electrons spread out before pairing up (Hund's Rule)
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Chapter-2-43Chemistry 481, Spring 2017, LA Tech
Molecular Orbital Theory • Molecular orbitals are obtained by combining the
atomic orbitals on the atoms in the molecule.
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Chapter-2-44Chemistry 481, Spring 2017, LA Tech
Bonding and Anti-bobding Molecular Orbital
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Chapter-2-45Chemistry 481, Spring 2017, LA Tech
Bond Order • Calculating Bond Order
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Chapter-2-46Chemistry 481, Spring 2017, LA Tech
Homo Nuclear Diatomic Molecules Period 1 Diatomic Molecules: H2 and He2
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Chapter-2-47Chemistry 481, Spring 2017, LA Tech
Homo Nuclear Diatomic Molecules Period 2 Diatomic Molecules and Li2 and Be2
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Chapter-2-48Chemistry 481, Spring 2017, LA Tech
Homo Nuclear Diatomic Molecules
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Chapter-2-49Chemistry 481, Spring 2017, LA Tech
Molecualr Orbital diagram for
B2, C2 and N2
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Chapter-2-50Chemistry 481, Spring 2017, LA Tech
Molecualr Orbital diagram for
O2, F2 and Ne2
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Chapter-2-51Chemistry 481, Spring 2017, LA Tech
7. Using molecular orbital theory and diagrams, explain why, O2 is a paramagnetic whereas N2 is diamagnetic.
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Chapter-2-52Chemistry 481, Spring 2017, LA Tech
Electronic Configuration of moleculesWhen writing the electron configuration of an
atom, we usually list the orbitals in the order in which they fill.
Pb: [Xe] 6s2 4f14 5d10 6p2
We can write the electron configuration of a molecule by doing the same thing. Concentrating only on the valence orbitals, we write the electron configuration of O2 as follows. O2: (2s) 2(2s*) 2 (2p) 4 (2p*) 2
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Chapter-2-53Chemistry 481, Spring 2017, LA Tech
Electronic Configuration and bond order
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Chapter-2-54Chemistry 481, Spring 2017, LA Tech
Electronic Configuration and bond order
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Chapter-2-55Chemistry 481, Spring 2017, LA Tech
Hetero Nuclear Diatomic Molecules Carbon monoxide CO
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Chapter-2-56Chemistry 481, Spring 2017, LA Tech
8. Draw molecular orbital diagrams for HF, CO, NO, NO+. Calculate their bond order and predict magnetic properties.
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Chapter-2-57Chemistry 481, Spring 2017, LA Tech
MO Correlation Diagrams ( Walsh Diagrams)• The correlation diagram clearly indicates that the
molecular orbital energy levels changes as the H3 changes from linear to cyclic (equilateral triangle) structure. In the case of
• linear H3 the overlap between two terminal H is minimal, where as in the case of cyclic H3 the overlap is substantial. This will bring the lowest MO (bonding) and the highest MO (antibonding) down in energy. At the same time, the non-bonding MO (middle one) will
• go up in energy, leading to a degenerate set of levels. Thus H3
+ (two electrons) will be triangular.
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Chapter-2-58Chemistry 481, Spring 2017, LA Tech
Walsh Diagram for H3:
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Chapter-2-59Chemistry 481, Spring 2017, LA Tech
9. Draw a molecular orbital diagram for triangular H3
+ and describe the bonding.
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Chapter-2-60Chemistry 481, Spring 2017, LA Tech
10. Draw a Walsh diagram (orbital correlation diagram) and show that triangular H3
+ is more stable than linear H3
+.
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Chapter-2-61Chemistry 481, Spring 2017, LA Tech
Conjugated and aromatic molecules• trans-1,3-Butadiene• Allyl radical • Cyclopropenium ion: C3H3
+
• Cyclobutadiene• Cyclopentadiene• Benzene• C7H7
+ (tropyllium) and C8H82+
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Chapter-2-62Chemistry 481, Spring 2017, LA Tech
trans-1,3-Butadiene
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Chapter-2-63Chemistry 481, Spring 2017, LA Tech
Allyl radical
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Chapter-2-64Chemistry 481, Spring 2017, LA Tech
Cyclopropenium ion: C3H3+
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Chapter-2-65Chemistry 481, Spring 2017, LA Tech
Cyclopentadiene
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Chapter-2-66Chemistry 481, Spring 2017, LA Tech
Benzene
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Chapter-2-67Chemistry 481, Spring 2017, LA Tech
Aromatic Rings
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Chapter-2-68Chemistry 481, Spring 2017, LA Tech
11. Using molecular orbital diagrams for pi (p) orbitals explain the relative stabilities of the following: (a) C3H3 and C3H3
+ (b) C4H4 and C4H4
+ (c) C5H5 and C5H5
- (d) C6H6 and C6H6
+ (e) C7H7 and C7H7
+
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Chapter-2-69Chemistry 481, Spring 2017, LA Tech
The Isolobal Analogy• Different groups of atoms can give rise to
similar shaped fragments.
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Chapter-2-70Chemistry 481, Spring 2017, LA Tech
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Chapter-2-71Chemistry 481, Spring 2017, LA Tech
12. Pick the isolobal fragments among the following:a) Co3(CO)9Co(CO) 3, Co3(CO)9PR, Co3(CO)9CH
b) H3CCl, Mn(CO)5H, Re(CO) 5Cl
c) R2SiH2, Fe(CO)4H2, H2CH2
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Chapter-2-72Chemistry 481, Spring 2017, LA Tech
Metallic Bonding
• Metals are held together by delocalized bonds formed from the atomic orbitals of all the atoms in the lattice.
• The idea that the molecular orbitals of the band of energy levels are spread or delocalized over the atoms of the piece of metal accounts for bonding in metallic solids.
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Chapter-2-73Chemistry 481, Spring 2017, LA Tech
Linear Combination of Atomic Orbitals
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Chapter-2-74Chemistry 481, Spring 2017, LA Tech
Bonding Models for Metals
•Band Theory of Bonding in Solids
•Bonding in solids such as metals, insulators and semiconductors may be understood most effectively by an expansion of simple MO theory to assemblages of scores of atoms
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Chapter-2-75Chemistry 481, Spring 2017, LA Tech
Linear Combination of Atomic Orbitals
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Chapter-2-76Chemistry 481, Spring 2017, LA Tech
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Chapter-2-77Chemistry 481, Spring 2017, LA Tech
Band Theory of Metals
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Chapter-2-78Chemistry 481, Spring 2017, LA Tech
13. Describe metallic bonding and properties in terms of: a) Electron-sea model of bonding: b) Band Theory:
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Chapter-2-79Chemistry 481, Spring 2017, LA Tech
14. Draw the s band (molecular orbitals) for ten Na on a line (one dimensional) and show bonding and anti-bonding molecular orbitals and fill electrons.
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Chapter-2-80Chemistry 481, Spring 2017, LA Tech
15. Describe the metallic properties of sodium in terms of band theory.
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Chapter-2-81Chemistry 481, Spring 2017, LA Tech
16. Using a band diagram, explain how magnesium can exhibit metallic behavior even though its 3s band is completely full.
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Chapter-2-82Chemistry 481, Spring 2017, LA Tech
Types of Materials• A conductor (which is usually a metal) is a
solid with a partially full band• An insulator is a solid with a full band and
a large band gap• A semiconductor is a solid with a full band
and a small band gap• Element Band Gap
C 5.47 eVSi 1.12 eVGe 0.66 eVSn 0 eV
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Chapter-2-83Chemistry 481, Spring 2017, LA Tech
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Chapter-2-84Chemistry 481, Spring 2017, LA Tech
17. Draw a Band diagram for carbon/silicon/germanium/tin, and label valence band, conduction band and band gap?
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Chapter-2-85Chemistry 481, Spring 2017, LA Tech
18. Draw a band diagrams to show the difference between(Band gaps: C = 5.47, Si = 1.12, Ge = 0.66, Sn = 0)
Conductor (Sn):
Insulator (C):
Semiconductor (Ge):
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Chapter-2-86Chemistry 481, Spring 2017, LA Tech
19. Draw a band diagram for thermal/photo (Intrinsic) and doped (Extrinsic) semiconductors and explain the origin of semicondictivity?
Thermal/photo (Intrinsic) (Ge):
Doped (Extrinsic) (Si/As):
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Chapter-2-87Chemistry 481, Spring 2017, LA Tech
20. Draw a band diagram for a p-type (Si/Ga) and n-type (Si/As) semiconductors and show holes and electrons that is responsible for semiconductivity.
p-type(Si/Ga):
n-type(Si/As):
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Chapter-2-88Chemistry 481, Spring 2017, LA Tech
22. What the difference between a transistor (semiconductor device) and vacuum tube?
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Chapter-2-89Chemistry 481, Spring 2017, LA Tech
What is a transistor?
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Chapter-2-90Chemistry 481, Spring 2017, LA Tech
21. What is a transistor with emitter (E), collector(C) and base (B), and how it works?
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Chapter-2-91Chemistry 481, Spring 2017, LA Tech
23. Using the diagram explain how a diode work.
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Chapter-2-92Chemistry 481, Spring 2017, LA Tech
Superconductors• When Onnes cooled mercury to 4.15K, the
resistivity suddenly dropped to zero
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Chapter-2-93Chemistry 481, Spring 2017, LA Tech
The Meissner Effect
•Superconductors show perfect diamagnetism.•Meissner and Oschenfeld discovered that a superconducting material cooled below its critical temperature in a magnetic field excluded the magnetic flux. Results in levitation of the magnet in a magnetic field.
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Chapter-2-94Chemistry 481, Spring 2017, LA Tech
Theory of Superconduction•BCS theory was proposed by J. Bardeen, L. Cooper and J. R. Schrieffer. BCS suggests the formation of so-called 'Cooper pairs'
Cooper pair formation - electron-phonon interaction: the
electron is attracted to the positive charge density (red
glow) created by the first electron distorting the lattice
around itself.
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Chapter-2-95Chemistry 481, Spring 2017, LA Tech
High Temperature Superconduction•BCS theory predicted a theoretical maximum to Tc of around 30-40K. Above this, thermal energy would cause electron-phonon interactions of an energy too high to allow formation of or sustain Cooper pairs.
• 1986 saw the discovery of high temperature superconductors which broke this limit (the highest known today is in excess of 150K) - it is in debate as to what mechanism prevails at higher temperatures, as BCS cannot account for this.