Week 8/Th: Lecture Unit ‘20’

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Unit 19: Chemical Bonding -- Basis of bonding -- Ionic Bonds -- Electron sharing, Covalent Bonds Unit 20: Covalent Bonding -- Lewis Dots -- multiple bonds -- Lewis “structures” Issues: electron configurations ? Homework #6 due this Saturday, Oct. 20th 8am Exam #2 on next Monday, Oct. 22, 7:15pm !!

G.N. Lewis (1937) isolated “heavy water”

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★ Tuesday, October 16th, 6 - 8:30pm in N100 BCC (LRC Mock Exam, reservation required!)

★ Thursday, October 18th, 6 - 8:30pm in N100 BCC

(LRC Q&A Review Session) ★ Sunday, October 21st, 4 - 6pm in 138 Chemistry

(Dr. Pollock)

★ Monday, October 22nd, 7:15 PM, EXAM day for everyone

★ Tuesday, October 23rd, back here for lecture 11:20am

Week 8/Th: Help Preparing for Exam

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Week 8/Th: Where to Take the Exam

CEM 141 - Fall Semester 2012 – Exam 2 Rooms Monday, October 22nd 7:15pm-8:15pm

Alternate Exam Monday, October 22nd 6:45am-7:45am room 138 Chemistry

Section Room

1,2,3,4,5,6,7,8,9,10 N130 Business Complex 11,12,13,14,15,16,17,18,19,20 B115 Wells Hall

21,22,23,24,25,26,27 138 Chemistry 28,29,30,31 118 Psychology Bldg. 32,33,34,35 B117 Wells Hall

36,37,38,75,76 N100 Business Complex 39,40,41 128 Nat. Sci. Bldg.

42,43,44,45 1345 Engineering Bldg. 46,47,48,49,50,51,52,53 102 Conrad Hall

54,55,56,57,58,59,60,61,62,63 1281 Anthony Hall 64,65,66,67 402 Computer Center

68,69,70 1279 Anthony Hall 71,72,73,74 N101 North Kedzie 77,78,79,80 B119 Wells Hall 81,82,83,84 1410 BioMed & Phys. Sci

Week 8/Th: Electron Configurations

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1)  Valence electrons are shared in pairs between atoms. 2)  The number of electrons available to each atom in the

bond should be the same as the number of electrons in the next noble gas (usually 8).

Examples last time: Hydrogen, H2 à or or There are options for how you draw the structure …

Week 8/Th: Last time: Lewis Pair-Bond Theory

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H•

H•

H H

H H

H H

1)  Valence electrons are shared in pairs between atoms. 2)  The number of electrons available to each atom in the

bond should be the same as the number of electrons in the next noble gas (usually 8).

Examples: Water H2O Hydrogen peroxide H2O2

Week 8/Th: Last time: Lewis Pair-Bond Theory

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H•H•O O H

H

O H H

O

Examples continue: Methane, CH4 Ethanol, CH3CH2OH

Week 8/Th: Lewis Dot Diagrams -2-

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H•H•

C

O C

H H C H H

H•H•

H•H•

C H•H•

H•H•

H H H C C O H H H

Examples continue: Oxygen, O2 Formaldehyde, CH2O

Week 8/Th: Lewis Dot Diagrams -3-

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H•H•

••

••

C::••

••

OH

H

••

C::••

••

OH: H

O O

O H C H

O H C H

O C

O O O O

Examples continue: Nitrogen, N2 Ammonia, NH3 Phosphine, PH3 ?

Week 8/Th: Lewis Dot Diagrams -4-

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H• H• H•

N N

H H N H

H H N H

N

N N N N

Examples continue: Phosgene, COCl2 Related to CH2O ? ! Methane, CH4 must be related to CH3F, CHF3, CF4, CCl4 … for example:

Week 8/Th: Lewis Dot Diagrams -5-

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O C Cl

Cl

O Cl C Cl

O Cl C Cl

H H C H

H Cl F C F

F

Week 8/Th: Thermite Reaction – Exam Review

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2 Al (s) + Fe2O3 (s) à 2 Fe (s) + Al2O3 (s) + energy ? Redox: oxidation (increase) 2* [ Al 0 à +3 ] … Six electrons reduction (decrease) 2* [ Fe +3 à 0 ] and no change in oxidation number for oxygen Hess’s Law: 2 Al (s) + Fe2O3 (s) à 2 Fe (s) + Al2O3 (s) + energy ΔHo

f 2* 0 1* -826 2* 0 1* -1676 kJ ΔH = [0 + -1676 ] – [0 + -826 ] = -850 kJ as written ( large negative number, very exothermic ) Electron Configurations: 26Fe à1s22s22p63s23p64s23d6 13Al à1s22s22p63s23p1 or [Ar] 4s23d6 or [Ne] 3s23p1

8O à 1s22s22p4