Types of Bonding and Lewis Structures

1. 13 December 2011 • Objective: You will be able to: • describe the three types of bonding and determine which type of bonding is present in a compound • Do now: On the first slide of your handout, brainstorm everything you know about bonding. • Homework: p. 400 #5, 6, 16, 17, 20, 21 due tomorrow, will be checked

2. Agenda • Do now • Ionic vs. Covalent vs. Metallic Bonding Notes, Videos and Demo

3. Chemical Bonding • What do you know about bonding?

4. chemical bond: a strong force of attraction that holds two atoms together. Involves only the valence electrons.

5. Types of Bonds • ionic: attractive force between ions of opposite charges, often a metal cation and a non-metal anion. • covalent: results from sharing electrons between two atoms, usually non-metal atoms. • http://www.youtube.com/watch?v=QqjcCvzWwww • http://www.youtube.com/watch?v=yjge1WdCFPs • metallic: occurs when the nuclei of a collection of metal atoms simultaneously attract their collective electrons. • http://www.drkstreet.com/resources/metallic-bonding-animation.swf

8. Ionic or Covalent? • Why? Which have both ionic and covalent bonds? • KBr • SO2 • H2SO4 • CH3COOH • Na3PO4 • CaCO3

9. Lewis symbol • valance electrons as dots • Draw the Lewis symbol of the first 18 elements. • left, right, top, bottom, top, bottom left, right

10. octet rule: representative elements tend to gain, lose, or share electrons until they are surrounded by eight valence electrons (an octet) • This gives atoms noble gas configuration with full s and p sublevels • Noble gas configurations are very stable. • Hydrogen requires only two electrons to attain noble gas configuration

11. 14 December 2011 • Objective: You will be able to: • describe ionic and covalent bonding and draw Lewis structures for covalent compounds. • Homework Quiz: Week of Dec. 12 a. Draw dot diagrams for sodium and sulfur. b. Using arrows, show what happens to their valence electrons when they bond. c. Write the name of the compound formed.

12. Agenda • Homework Quiz • Homework answers • Isoelectronic ions • Ionic bonding and lattice energy • Covalent Bonding • Lewis Structures Homework: p. 401 #30, 35, 39, 41, 44

13. Isoelectronic • having the same electron configuration as a noble gas • When an element attains a noble gas configuration, does it turn into a noble gas? Why or why not? • Which are isoelectronic with one another? • N3-, K+, Ca2+, O2-, F-, Ne, Br-, Kr, Sc3+, Na+, Al3+, Se2-, Mg2+

15. Ionic Bonding • Ions form when electrons transfer from an atom of low ionization energy (usually a metal) to an atom of high electron affinity (usually a non-metal). • The electrostatic attraction between two oppositely charged ions = ionic bond • Crystal lattice demo • http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom1s2_11.swf

17. lattice: a stable, ordered, solid, 3D array of ions. • lattice energy, ∆Hlattice, is the energy required to completely separate a mole of solid ionic compound into its gaseous ions. KF(s) → K+(g) + F-(g) ∆Hlattice= +808 kJ/mol

19. Example Lattice Energies

20. Ions of Transition Metals • Remember that the d orbital fills before s • When a transition metal is ionized, it loses the s electrons before the d electrons • Fe [Ar] 3d6 4s2 • Fe2+ [Ar] 3d6 • Fe3+ [Ar] 3d5 • Write the electron configuration for Cr3+ and Sn4+

21. Covalent Bonding • formed between two atoms that share one or more pairs of electrons • Lewis structures show shared pairs of electrons (bonding pairs) • carbon dioxide:

22. Lewis Structures Rules • Total the valance electrons of all the bonded atoms • Use one pair of electrons to bond each outer atom to the central atom (usually the atom in least abundance) • Complete the octets around the outer atoms • Place any remaining electrons on the central atom • If there are not enough electrons to give the central atom an octet, make multiple bonds.

23. NO3-

24. Practice Problems • Br2 • CH4 • H2O • H2CO • SeF2 • CF4 • CHCl3 • CO2 • BF3 • SO3 • NH4+ • HCN

25. Resonance Structures • two or more Lewis structures that are equally good representations of the bonding in a molecule or ion. • Usually differ only in the positions of multiple or single bonds and unpaired electrons

26. Formal Charge • the number of valence electrons in an isolated atom minus the number of electrons assigned to the atom in the Lewis structure • Used to determine which Lewis structure is the most suitable to represent bonding • Choose the one closest to zero.

27. Steps to Formal Charge • Examine each atom one at a time. • Count both electrons in a lone pair (nonbonding electrons) and one electron per bond. • Compare this number with the group number. • If you have one less electron than the group # indicates, the charge is +1 One more electron than the group #, the charge is -1, etc.

28. Example: Nitrate Ion

29. Example: Ammonium Ion

30. Formal Charge Practice Problems • ClO3- • CHO2- • C2H3Cl

31. 19 December 2011 • Objective: You will be able to: • calculate bond energies and review chemical bonding • Homework Quiz: Draw two resonance structures for diazomethane, CH2N2. Show formal charges for both structures. The skeletal structure is: H C N N H

32. Agenda • Homework Quiz • Bond strength and enthalpy • Problem Set Homework: Problem Set due Weds.

33. Strengths of Covalent Bonds • ∆HBDE = bond dissociation energy (bond enthalpy) • the enthalpy change for the breaking of bonds in one mole of a gaseous substance • Bond breaking ∆H always positive, always endothermic • Bond making is exothermic!

34. ∆Hrxn = sum of the bond enthalpies of the broken bonds – sum of the bond enthalpies of the bonds formed • Multiple bonds are shorter and stronger than single bonds

35. Example • Use average bond enthalpies to estimate the enthalpy change of the following reaction: 2H2O → 2H2 + O2

36. Practice Problems • Calculate the enthalpy of reaction for the process: • H2(g) + Cl2(g) → 2HCl(g) • H2(g) + F2(g) → 2HF(g) • H2(g) + C2H4(g) → C2H6(g)

37. This week… • Today: Problem Set Work Time • Tomorrow: Green crystal lab part 1: reaction and growing crystals • Thurs: Green crystal lab parts 2 and 3: Washing and drying crystals • and problem set work time • Problem set due Tuesday after vacation • Vacation Assignment (distributed tomorrow) due Wednesday after vacation

38. 21 December 2011 • Objective: You will be able to: • synthesize a green crystal for later analysis • Do now: • Grab a pair of goggles and sit with your lab partner. • Take out the lab packet.

39. Reaction and reagents • iron (III) chloride hexahydrate with potassium oxalate • iron (III) chloride is a brown solution at the front lab tables • pipette 8 mL • potassium oxalate is a white crystal at the side lab tables • weigh 12 grams on weighing paper • distilled water is in the wash bottles • ice is in the white coolers at the front – you can put your product beaker directly into the cooler

40. Work quickly • Your product needs to chill for about 30 minutes before you pour off the solvent and redissolve your crystals! • We’ll store the crystals in a sample bottle tomorrow. • Work on your problem set while you wait. • For now, collect data on your lab handout.

41. 22 December 2011 • Objective: You will be able to: • separate your crystal from the solution and dry it

42. Winter Break Assignment • Liquids and Intermolecular Forces • Read pages 461-472 and 489-499 • Complete the following problems by Tuesday, Jan. 3: • page 504 #1, 2, 5, 6, 7, 10, 12, 14, 16, 18, 21, 22, 24, 25, 59, 60, 62, 66, 70, 72, 73, 79, 81, 85, 91, 94

43. Today • Watch demo of vacuum filtration. • Complete Day 2 and Day 3 of experiment • Work on problem set in pairs • work efficiently and quietly • stay in your seat unless you need to move around for the lab