Chemistry 481(01) Spring 2014

1. Chemistry 481(01) Spring 2014 • 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 10:00 - 12:00 a.m. • April 10 , 2014: Test 1 (Chapters 1,  2, 3,) • May 1, 2014: Test 2 (Chapters  5, 6 & 7) • May 20, 2014: Test 3 (Chapters. 19 & 20) • May 22, Make Up: Comprehensive covering all Chapters

2. 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

3. 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

4. How do you get the Lewis Structure from Molecular formula? • 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)

5. 1. Draw Lewis structure for SbF5, ClF3, and IF6+:

6. 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

7. 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

8. 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)

9. 2. Predict geometry of central atom using VSEPR and the hybridization in problem 1. SbF5, ClF3, and IF6+:

10. 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

11. Formal Charge Calculation An arithmetic formula for calculating formal charge. Formal charge = number ofbonds number ofunshared electrons group numberin periodic table – –

12. Electron counts" and formal charges in NH4+ and BF4- "

13. Resonance structures of SO2 They both are! 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

14. Resonance structures of CO32- ion

15. 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

16. 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.

17. 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 theto from sigma (s) , pi (p) bonds and (d) bonds

18. Linear Combination of Atomic Orbitals Symmetry 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

19. 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

20. 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

21. Kinds of hybrid orbitals Hybrid geometry # of orbital sp linear 2 sp2 trigonal planar 3 sp3 tetrahedral 4 sp3d trigonalbipyramid 5 sp3d2 octahedral 6

22. 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 dx2- y2 Py Pz dz2

23. Possible hybridizations of s and p • sp-hybridization: • y1 = 1/Ö2ys - 1/Ö2ypy2 = 1/Ö2ys + 1/Ö2yp • sp2-hybridization: • y1 = 1/Ö3ys + 1/Ö6ypx + 1/Ö2ypyy2 = 1/Ö3ys + 1/Ö6ypx - 1/Ö2ypyy3 = 1/Ö3ys - 2/Ö6ypx • sp3-hybridization: • y1 = 1/Ö4ys + 1/Ö4ypx + 1/Ö4ypy + 1/Ö4ypzy2 = 1/Ö4ys - 1/Ö4ypx - 1/Ö4ypy + 1/Ö4ypzy3 = 1/Ö4ys + 1/Ö4ypx - 1/Ö4ypy - 1/Ö4ypzy4 = 1/Ö4ys - 1/Ö4ypx + 1/Ö4ypy -1/Ö4ypz

24. Possible hybridizations of s and p sp-hybridization:

25. What are p and s bonds s bonds single bond resulting from head to head overlap of atomic orbital p bond double and triple bond resulting from lateral or side way overlap of p atomic orbitals dbond double and triple bond resulting from lateral or side way overlap of d atomic orbitals

26. 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 dorbitals 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

27. 3. Why hypervalent compounds are formed by elements such as Si, P and S, but not by C,N and O?

28. O O S O O O || O S O - - || O An example: SO42- 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.

29. : : :Cl:Be:Cl: : : Atoms with fewer than eight electrons Beryllium and boron will both form compounds where they have less than 8 electrons around them. : : :F:B:F: :F: : : : :

30. H | :N – H | H F | B | F F H | | F - B <- N - H | | F H F - + 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.

31. 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

32. How do you a Pick Polar Molecule? • Get the molecular structure from VSEPR theory • From c (electronegativity) difference of bonds see whether they are polar-covalent. • If the molecule have polar-covalent bond, check whether they cancel from a symmetric arrangement. • If not molecule is polar Predicting symmetry of molecule and the polarity will be discussed in detail in Chapter 7.

33. Linear Combination of Atomic Orbitals Symmetry 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

34. 6. Draw a diagram to illustrate each described overlap: a) s bonding overlap of two p orbitals b) dbonding overlap of two d orbitals c) pbonding overlap of a p orbital and a d orbital d) santibonding overlap of a p and a d orbital e) dantibonding overlap of two d orbitals.

35. What are p and s bonds s bonds p bond

36. What are d bonds dbond double and triple bond resulting from lateral or side way overlap of d atomic orbitals

37. Kinds of hybrid orbitals Hybrid geometry # of orbital sp linear 2 sp2 trigonal planar 3 sp3 tetrahedral 4 sp3d trigonalbipyramid 5 sp3d2 octahedral 6

38. 5. Using valence-bond (VB) theory to explain the bonding in the coordination complex ion, Co(NH3)63+.

39. Hybridization involving d orbitals • Co(NH3)63+ 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

40. 5.  What is the oxidation state of metal in (a) Co(NH3)63+ ion (b) PtCl42- ion. • [Co(NH3)6]3+ Co3+and NH3is neutral Oxidation Sate of Co3+ is +3 and NH3 is 0 Therefore sum of the oxidation should be equal to +3 +3= Co(NH3)6 =(Co)3+6((NH3)0)= +3 Co is +3 in [Co(NH3)6]3+ b) Pt is +2 in [PtCl4]2- becauseCl- is -1

41. Linear Combination of Atomic Orbitals Symmetry 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

42. Basic Rules of Molecular Orbital Theory The 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)

43. Molecular Orbital Theory • Molecular orbitals are obtained by combining the atomic orbitals on the atoms in the molecule.

44. Bonding and Anti-bobding Molecular Orbital

45. Bond Order • Calculating Bond Order

46. Homo Nuclear Diatomic Molecules Period 1 Diatomic Molecules: H2 and He2

47. Homo Nuclear Diatomic Molecules Period 2 Diatomic Molecules and Li2 and Be2

48. Homo Nuclear Diatomic Molecules

49. Molecualr Orbital diagram for B2, C2 and N2

50. Molecualr Orbital diagram for O2, F2 and Ne2