2. Chapter-2-1 Chemistry 481, Spring 2014, LA Tech Instructor: Dr. Upali Siriwardane e-mail: upali@latech.edu 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 7, 2015: Test 1 (Chapters 1, 2, 3) April 30, 2015: Test 2 (Chapters 5, 6 & 7) May 19, 2015: Test 3 (Chapters. 19 & 20) May 19, Make Up: Comprehensive covering all Chapters Chemistry 481(01) Spring 2015

3. Chapter-2-2 Chemistry 481, Spring 2014, 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 diatomic 2.10 Bond properties

4. Chapter-2-3 Chemistry 481, Spring 2014, 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

5. Chapter-2-4 Chemistry 481, Spring 2014, 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?

6. Chapter-2-5 Chemistry 481, Spring 2014, LA Tech 1. Draw Lewis structure for SbF 5, ClF 3, and IF 6 + :

7. Chapter-2-6 Chemistry 481, Spring 2014, LA Tech What is VSEPR Theory Valence Shell Electron Pair Repulsion This theory assumes that the molecular structure is determined by the lone pair and bond pair electron repulsion around the central atom

8. Chapter-2-7 Chemistry 481, Spring 2014, LA Tech What Geometry is Possible around Central Atom? What is Electronic or Basic Structure? What is Electronic or Basic Structure? Arrangement of electron pairs around the central atom is called the electronic or basic structure Arrangement of electron pairs around the central atom is called the electronic or basic structure What is Molecular Structure? What is Molecular Structure? Arrangement of atoms around the central atom is called the molecular structure Arrangement of atoms around the central atom is called the molecular structure

9. Chapter-2-8 Chemistry 481, Spring 2014, LA Tech Possible Molecular Geometry Linear (180) Linear (180) Trigonal Planar (120) Trigonal Planar (120) T-shape (90, 180) T-shape (90, 180) Tetrahedral (109) Tetrahedral (109) Square palnar ( 90, 180) Square palnar ( 90, 180) Sea-saw (90, 120, 180) Sea-saw (90, 120, 180) Trigonal bipyramid (90, 120, 180) Trigonal bipyramid (90, 120, 180) Octahedral (90, 180) Octahedral (90, 180)

10. Chapter-2-9 Chemistry 481, Spring 2014, LA Tech 2. Predict geometry of central atom using VSEPR and the hybridization in problem 1. SbF 5, ClF 3, and IF 6 + :

11. Chapter-2-10 Chemistry 481, Spring 2014, LA Tech Formal Charges Formal charge = valence electrons - assigned electrons If 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 (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

12. Chapter-2-11 Chemistry 481, Spring 2014, 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.

13. Chapter-2-12 Chemistry 481, Spring 2014, LA Tech Electron counts" and formal charges in NH 4 + and BF 4 - "

14. Chapter-2-13 Chemistry 481, Spring 2014, LA Tech They both are! O - S = O O = S - O O - S = O O = S - O O S O O S O This 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 SO 2

15. Chapter-2-14 Chemistry 481, Spring 2014, LA Tech Resonance structures of CO 3 2- ion

16. Chapter-2-15 Chemistry 481, Spring 2014, LA Tech Resonance structures of C 6 H 6 Benzene, C 6 H 6, is another example of a compound for which resonance structure must be written. Benzene, C 6 H 6, is another example of a compound for which resonance structure must be written. All of the bonds are the same length. All of the bonds are the same length. or

17. Chapter-2-16 Chemistry 481, Spring 2014, LA Tech Exceptions to the octet rule Not all compounds obey the octet rule. Three types of exceptions Three types of exceptions Species with more than eight electrons around an atom. Species with more than eight electrons around an atom. Species with fewer than eight electrons around an atom. Species with fewer than eight electrons around an atom. Species with an odd total number of electrons. Species with an odd total number of electrons.

18. Chapter-2-17 Chemistry 481, Spring 2014, 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 , pi  bonds and  bonds

19. Chapter-2-18 Chemistry 481, Spring 2014, LA Tech Linear Combination of Atomic Orbitals Symmetry Adapted Linear Combination of Atomic Orbitals –LCAO Atomic orbitals on single atom Atomic orbitals on single atom: Hybridization Atomic orbitals in a molecule with more than one atom 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

20. Chapter-2-19 Chemistry 481, Spring 2014, 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, sp 2, sp 3, sp 3 d, sp 3 d 2

21. Chapter-2-20 Chemistry 481, Spring 2014, LA Tech How do you tell the hybridization of a central atom? Get the Lewis structure of the molecule 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. 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 Follow the following chart

22. Chapter-2-21 Chemistry 481, Spring 2014, LA Tech Kinds of hybrid orbitals Hybridgeometry# of orbital sp linear2 sp linear2 sp 2 trigonal planar3 sp 3 tetrahedral4 sp 3 d trigonal bipyramid5 sp 3 d 2 octahedral6

23. Chapter-2-22 Chemistry 481, Spring 2014, LA Tech What is hybridization? Mixing of atomic orbitals on the central atoms valence shell (highest n orbitals) Bonding: s p d sp, sp 2, sp 3, sp 3 d, sp 3 d 2 PxPx PyPy PzPz dz2dz2 d x 2 - y 2

24. Chapter-2-23 Chemistry 481, Spring 2014, LA Tech Possible hybridizations of s and p sp-hybridization:  1 = 1/  2  s - 1/  2  p  2 = 1/  2  s + 1/  2  p sp 2 -hybridization:  1 = 1/  3  s + 1/  6  px + 1/  2  py  2 = 1/  3  s + 1/  6  px - 1/  2  py  3 = 1/  3  s - 2/  6  px sp 3 -hybridization:  1 = 1/  4  s + 1/  4  px + 1/  4  py + 1/  4  pz  2 = 1/  4  s - 1/  4  px - 1/  4  py + 1/  4  pz  3 = 1/  4  s + 1/  4  px - 1/  4  py - 1/  4  pz  4 = 1/  4  s - 1/  4  px + 1/  4  py -1/  4  pz

25. Chapter-2-24 Chemistry 481, Spring 2014, LA Tech Possible hybridizations of s and p sp-hybridization:

26. Chapter-2-25 Chemistry 481, Spring 2014, LA Tech What are  and  bonds  bonds single bond resulting from head to head overlap of atomic orbital  bond double and triple bond resulting from lateral or side way overlap of p atomic orbitals  bond double and triple bond resulting from lateral or side way overlap of d atomic orbitals

27. Chapter-2-26 Chemistry 481, Spring 2014, LA Tech Atoms with more than eight electrons Except for species that contain hydrogen, this is the most common type of exception. 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. For elements in the third period and beyond, the d orbitals can become involved in bonding.Examples 5 electron pairs around P in PF 5 5 electron pairs around P in PF 5 5 electron pairs around S in SF 4 5 electron pairs around S in SF 4 6 electron pairs around S in SF 6 6 electron pairs around S in SF 6

28. Chapter-2-27 Chemistry 481, Spring 2014, LA Tech 3. Why hypervalent compounds are formed by elements such as Si, P and S, but not by C,N and O?

29. Chapter-2-28 Chemistry 481, Spring 2014, LA Tech An example: SO 4 2- 1. Write a possible arrangement. 2. Total the electrons. 6 from S, 4 x 6 from O add 2 for charge total = 32 3. Spread the electrons around. SO O O O - - || SO O O O

30. Chapter-2-29 Chemistry 481, Spring 2014, 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: : : : : : :

31. Chapter-2-30 Chemistry 481, Spring 2014, 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|FF|B|F F - + H | :N – H | H F H | | F - B <- N - H | | F H

32. Chapter-2-31 Chemistry 481, Spring 2014, LA Tech What is a Polar Molecule? Molecules with unbalanced electrical charges Molecules with unbalanced electrical charges Molecules with a dipole moment Molecules with a dipole moment Molecules without a dipole moment are called non-polar molecules Molecules without a dipole moment are called non-polar molecules

33. Chapter-2-32 Chemistry 481, Spring 2014, LA Tech How do you a Pick Polar Molecule? a) Get the molecular structure from VSEPR theory b) From  (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.

34. Chapter-2-33 Chemistry 481, Spring 2014, LA Tech Linear Combination of Atomic Orbitals Symmetry Adapted Linear Combination of Atomic Orbitals –LCAO Atomic orbitals on single atom Atomic orbitals on single atom: Hybridization Atomic orbitals in a molecule with more than one atom 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

35. Chapter-2-34 Chemistry 481, Spring 2014, LA Tech 6. Draw a diagram to illustrate each described overlap: a)  bonding overlap of two p orbitals b)  bonding overlap of two d orbitals c)  bonding overlap of a p orbital and a d orbital d)  antibonding overlap of a p and a d orbital e)  antibonding overlap of two d orbitals.

36. Chapter-2-35 Chemistry 481, Spring 2014, LA Tech What are  and  bonds  bonds  bond

37. Chapter-2-36 Chemistry 481, Spring 2014, LA Tech What are  bonds  bond double and triple bond resulting from lateral or side way overlap of d atomic orbitals

38. Chapter-2-37 Chemistry 481, Spring 2014, LA Tech Kinds of hybrid orbitals Hybridgeometry# of orbital sp linear2 sp linear2 sp 2 trigonal planar3 sp 3 tetrahedral4 sp 3 d trigonal bipyramid5 sp 3 d 2 octahedral6

39. Chapter-2-38 Chemistry 481, Spring 2014, LA Tech 5. Using valence-bond (VB) theory to explain the bonding in the coordination complex ion, Co(NH 3 ) 6 3+.

40. Chapter-2-39 Chemistry 481, Spring 2014, LA Tech Hybridization involving d orbitals Co(NH 3 ) 6 3+ ion Co 3+ : [Ar] 3d 6 Co(NH 3 ) 6 3+ ion Co 3+ : [Ar] 3d 6 Co 3+ : [Ar] 3d 6 4s 0 4p 0 Co 3+ : [Ar] 3d 6 4s 0 4p 0 Concentrating the 3d electrons in the d xy, d xz, and d yz orbitals in this subshell gives the following electron configuration hybridization is sp 3 d 2 Concentrating the 3d electrons in the d xy, d xz, and d yz orbitals in this subshell gives the following electron configuration hybridization is sp 3 d 2

41. Chapter-2-40 Chemistry 481, Spring 2014, LA Tech 5. What is the oxidation state of metal in (a) Co(NH 3 ) 6 3+ ion (b) PtCl 4 2- ion. a) a) [Co(NH 3 ) 6 ] 3+ Co 3+ and NH 3 is neutral Oxidation Sate of Co 3+ is +3 and NH 3 is 0 Therefore sum of the oxidation should be equal to +3 +3= Co(NH 3 ) 6 = (Co)3+6((NH 3 )0)= +3 Co is +3 in [Co(NH 3 ) 6 ] 3+ b) Pt is +2 in [ b) Pt is +2 in [PtCl 4 ] 2- because Cl - is -1

42. Chapter-2-41 Chemistry 481, Spring 2014, LA Tech Linear Combination of Atomic Orbitals Symmetry Adapted Linear Combination of Atomic Orbitals –LCAO Atomic orbitals on single atom Atomic orbitals on single atom: Hybridization Atomic orbitals in a molecule with more than one atom 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

43. Chapter-2-42 Chemistry 481, Spring 2014, LA Tech Basic Rules of Molecular Orbital Theory The MO Theory has five basic rules: The number of molecular orbitals = the number of atomic orbitals combined 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) 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 Electrons enter the lowest orbital available The maximum # of electrons in an orbital is 2 (Pauli Exclusion Principle) The maximum # of electrons in an orbital is 2 (Pauli Exclusion Principle) Electrons spread out before pairing up (Hund's Rule) Electrons spread out before pairing up (Hund's Rule)

44. Chapter-2-43 Chemistry 481, Spring 2014, LA Tech Molecular Orbital Theory Molecular orbitals are obtained by combining the atomic orbitals on the atoms in the molecule. Molecular orbitals are obtained by combining the atomic orbitals on the atoms in the molecule.

45. Chapter-2-44 Chemistry 481, Spring 2014, LA Tech Bonding and Anti-bobding Molecular Orbital

46. Chapter-2-45 Chemistry 481, Spring 2014, LA Tech Bond Order Calculating Bond Order Calculating Bond Order

47. Chapter-2-46 Chemistry 481, Spring 2014, LA Tech Homo Nuclear Diatomic Molecules Period 1 Diatomic Molecules: H 2 and He 2

48. Chapter-2-47 Chemistry 481, Spring 2014, LA Tech Homo Nuclear Diatomic Molecules Period 2 Diatomic Molecules and Li 2 and Be 2

49. Chapter-2-48 Chemistry 481, Spring 2014, LA Tech Homo Nuclear Diatomic Molecules

50. Chapter-2-49 Chemistry 481, Spring 2014, LA Tech Molecualr Orbital diagram for B 2, C 2 and N 2

51. Chapter-2-50 Chemistry 481, Spring 2014, LA Tech Molecualr Orbital diagram for O 2, F 2 and Ne 2

52. Chapter-2-51 Chemistry 481, Spring 2014, LA Tech 7. Using molecular orbital theory and diagrams, explain why, O 2 is a paramagnetic whereas N 2 is diamagnetic.

53. Chapter-2-52 Chemistry 481, Spring 2014, LA Tech Electronic Configuration of molecules When writing the electron configuration of an atom, we usually list the orbitals in the order in which they fill. Pb: [Xe] 6s 2 4f 14 5d 10 6p 2 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 O 2 as follows. O 2 : ( 2  2 (2  *) 2 (2  4 (2  *  2

54. Chapter-2-53 Chemistry 481, Spring 2014, LA Tech Electronic Configuration and bond order

55. Chapter-2-54 Chemistry 481, Spring 2014, LA Tech Electronic Configuration and bond order

56. Chapter-2-55 Chemistry 481, Spring 2014, LA Tech Hetero Nuclear Diatomic Molecules Carbon monoxide CO

57. Chapter-2-56 Chemistry 481, Spring 2014, LA Tech 8. Draw molecular orbital diagrams for HF, CO, NO, NO +. Calculate their bond order and predict magnetic properties.

58. Chapter-2-57 Chemistry 481, Spring 2014, LA Tech MO Correlation Diagrams ( Walsh Diagrams) The correlation diagram clearly indicates that the molecular orbital energy levels changes as the H 3 changes from linear to cyclic (equilateral triangle) structure. In the case of The correlation diagram clearly indicates that the molecular orbital energy levels changes as the H 3 changes from linear to cyclic (equilateral triangle) structure. In the case of linear H 3 the overlap between two terminal H is minimal, where as in the case of cyclic H 3 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 linear H 3 the overlap between two terminal H is minimal, where as in the case of cyclic H 3 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 H 3 + (two electrons) will be triangular. go up in energy, leading to a degenerate set of levels. Thus H 3 + (two electrons) will be triangular.

59. Chapter-2-58 Chemistry 481, Spring 2014, LA Tech Walsh Diagram for H 3 :

60. Chapter-2-59 Chemistry 481, Spring 2014, LA Tech 9. Draw a molecular orbital diagram for triangular H 3 + and describe the bonding.

61. Chapter-2-60 Chemistry 481, Spring 2014, LA Tech 10. Draw a Walsh diagram (orbital correlation diagram) and show that triangular H 3 + is more stable than linear H 3 +.

62. Chapter-2-61 Chemistry 481, Spring 2014, LA Tech Conjugated and aromatic molecules trans-1,3-Butadiene trans-1,3-Butadiene Allyl radical Allyl radical Cyclopropenium ion: C 3 H 3 + Cyclopropenium ion: C 3 H 3 + Cyclobutadiene Cyclobutadiene Cyclopentadiene Cyclopentadiene Benzene Benzene C 7 H 7 + (tropyllium) and C 8 H 8 2+ C 7 H 7 + (tropyllium) and C 8 H 8 2+

63. Chapter-2-62 Chemistry 481, Spring 2014, LA Tech trans - 1,3-Butadiene

64. Chapter-2-63 Chemistry 481, Spring 2014, LA Tech Allyl radical

65. Chapter-2-64 Chemistry 481, Spring 2014, LA Tech Cyclopropenium ion: C 3 H 3 +

66. Chapter-2-65 Chemistry 481, Spring 2014, LA Tech Cyclopentadiene

67. Chapter-2-66 Chemistry 481, Spring 2014, LA Tech Benzene

68. Chapter-2-67 Chemistry 481, Spring 2014, LA Tech Aromatic Rings

69. Chapter-2-68 Chemistry 481, Spring 2014, LA Tech 11. Using molecular orbital diagrams for pi (p) orbitals explain the relative stabilities of the following: (a) C 3 H 3 and C 3 H 3 + (b) C 4 H 4 and C 4 H 4 + (c) C 5 H 5 and C 5 H 5 - (d) C 6 H 6 and C 6 H 6 + (e) C 7 H 7 and C 7 H 7 +

70. Chapter-2-69 Chemistry 481, Spring 2014, LA Tech The Isolobal Analogy Different groups of atoms can give rise to similar shaped fragments. Different groups of atoms can give rise to similar shaped fragments.

71. Chapter-2-70 Chemistry 481, Spring 2014, LA Tech

72. Chapter-2-71 Chemistry 481, Spring 2014, LA Tech 12. Pick the isolobal fragments among the following: a) Co 3 (CO) 9 Co(CO) 3, Co 3 (CO) 9 PR, Co 3 (CO) 9 CH b) H 3 CCl, Mn(CO) 5 H, Re(CO) 5 Cl c) R 2 SiH 2, Fe(CO) 4 H 2, H 2 CH 2

73. Chapter-2-72 Chemistry 481, Spring 2014, LA Tech Metallic Bonding Metals are held together by delocalized bonds formed from the atomic orbitals of all the atoms in the lattice. 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. 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.

74. Chapter-2-73 Chemistry 481, Spring 2014, LA Tech Linear Combination of Atomic Orbitals

75. Chapter-2-74 Chemistry 481, Spring 2014, LA Tech Bonding Models for Metals Band Theory of Bonding in Solids 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 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

76. Chapter-2-75 Chemistry 481, Spring 2014, LA Tech Linear Combination of Atomic Orbitals

77. Chapter-2-76 Chemistry 481, Spring 2014, LA Tech

78. Chapter-2-77 Chemistry 481, Spring 2014, LA Tech Band Theory of Metals

79. Chapter-2-78 Chemistry 481, Spring 2014, LA Tech 13. Describe metallic bonding and properties in terms of: a) Electron-sea model of bonding: b) Band Theory:

80. Chapter-2-79 Chemistry 481, Spring 2014, 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.

81. Chapter-2-80 Chemistry 481, Spring 2014, LA Tech 15. Describe the metallic properties of sodium in terms of band theory.

82. Chapter-2-81 Chemistry 481, Spring 2014, LA Tech 16. Using a band diagram, explain how magnesium can exhibit metallic behavior even though its 3s band is completely full.

83. Chapter-2-82 Chemistry 481, Spring 2014, LA Tech Types of Materials A conductor (which is usually a metal) is a solid with a partially full band 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 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 A semiconductor is a solid with a full band and a small band gap Element Band Gap C 5.47 eV Si 1.12 eV Ge 0.66 eV Sn 0 eV Element Band Gap C 5.47 eV Si 1.12 eV Ge 0.66 eV Sn 0 eV

84. Chapter-2-83 Chemistry 481, Spring 2014, LA Tech

85. Chapter-2-84 Chemistry 481, Spring 2014, LA Tech 17. Draw a Band diagram for carbon/silicon/germanium/tin, and label valence band, conduction band and band gap?

86. Chapter-2-85 Chemistry 481, Spring 2014, 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):

87. Chapter-2-86 Chemistry 481, Spring 2014, 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):

88. Chapter-2-87 Chemistry 481, Spring 2014, 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):

89. Chapter-2-88 Chemistry 481, Spring 2014, LA Tech 22. What the difference between a transistor (semiconductor device) and vacuum tube?

90. Chapter-2-89 Chemistry 481, Spring 2014, LA Tech What is a transistor?

91. Chapter-2-90 Chemistry 481, Spring 2014, LA Tech 21. What is a transistor with emitter (E), collector(C) and base (B), and how it works?

92. Chapter-2-91 Chemistry 481, Spring 2014, LA Tech 23. Using the diagram explain how a diode work.

93. Chapter-2-92 Chemistry 481, Spring 2014, LA Tech Superconductors When Onnes cooled mercury to 4.15K, the resistivity suddenly dropped to zero When Onnes cooled mercury to 4.15K, the resistivity suddenly dropped to zero

94. Chapter-2-93 Chemistry 481, Spring 2014, LA Tech The Meissner Effect Superconductors show perfect diamagnetism. 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. 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.

95. Chapter-2-94 Chemistry 481, Spring 2014, 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' 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.

96. Chapter-2-95 Chemistry 481, Spring 2014, 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. 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. 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.