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Chemistry 111

Cinco de Mayo, 2004

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Exam 1 Results

• Average: – M/C: 81.8% (21.5)– Lab: 72.9% (14.9)– Overall: 80.0%

• Median: 82.4!

• Max: 96.8%Grade #A 8B 15C 5

Exam 1 Histogram - Raw

012345678

35-40

40-45

45-50

50-55

55-60

60-65

65-70

70-75

75-80

80-85

85-90

90-95

95-100

Score

Co

un

t

WOW

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VSEPR & Molecular Polarity

• Bond Polarity (1 more detail)• Movie - VSEPR• Summary / Table• Work flow

• Movie – Polarity– CHCl3

– CH2Cl2

• Exams given back in lab or after class (in you don’t have lab today)

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Bond Polarity

• When a bond is polar (has EN), we use the “dipole” symbol.

• Just an arrow with a (+) on it’s butt tail.

• The arrow points to the higher EN atom.

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Movie About VSEPR

• We’ll study up to Tetrahedral• 2 Methods to know shape:

– Harder = memorize table 12.2 (pg. 327)– Easier? = learn a few steps (smaller

tables)1. Determine Lewis Structure2. Count “electron domains”3. Look up in Table4. Logically hide any lone pairs and determine

molecular shape.

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First VSEPR Table

# of Electron Domains

VSEPR Shape Bond Angle

2 Linear 180°

3 Trigonal Planar

120°

4 Tetrahedral 109.5°

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Hiding Lone Pairs

VSEPR Shape

# of Lone Pairs

Shape Angle Example

Trigonal Planar

1 “bent” < 120° SO2

Tetrahedral 2 “bent” < 109.5°

H2O, H2S

Tetrahedral 1 Trigonal Pyramid

< 109.5°

NH3

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Another Skill• Make sure you can do a 3-D sketch

of the tetrahedral molecule:3 atoms in Add 1 in front

3-Dthe plane & 1 behind

Model

C

F

F

C

F

F

F

F

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Movie – Molecular Polarity