1. Molecular Geometry Part 2
Multiple Bonds, Multiple Centers, Exceptions, and Polarity

2. Objective
Today I will be able to:
Summarize the exceptions and inner workings of molecular geometries
Draw Lewis Structures to represent the valance electrons of atoms
Predict the molecular shape of a molecule using the VSEPR theory
Evaluation/ Assessment
Informal assessment – Listening to group interactions as they complete the illustrating ionic and covalent compounds practice and the molecular shapes lab.
Formal Assessment – Analyzing student responses to the exit ticket and the practice worksheets.
Common Core Connection
Make sense of problem and persevere in solving them
Reason abstractly and quantitatively
Use appropriate tools strategically
Look for and make use of structure

3. Lesson Sequence Warm – Up Explain: Exceptions and Polarity notes
Explore and elaborate: Molecular Shapes Lab
Informal Assessment
Evaluate: Exit Ticket
Formal assessment

4. Objective
Today I will be able to:
Summarize the exceptions and inner workings of molecular geometries
Draw Lewis Structures to represent the valance electrons of atoms
Predict the molecular shape of a molecule using the VSEPR theory

5. Homework
STEM Fair
In Class Presentations Wednesday January 22

6. Agenda Warm-Up Exceptions & Polarity Notes Molecular Shapes Lab
Exit Ticket

7. Warm-Up Which shape has the largest bond angle?
How many lone pairs and bonds formed are in the trigonal pyramidal shape?
Draw the molecular shape for phosphorus pentachloride.

8. Sample Problem 1
Writing Lewis Structures for Molecules with One Central Atom
PROBLEM:
Write a Lewis structure for CCl2F2

9. Sample Problem 2
Writing Lewis Structures for Molecules with More than One Central Atom
PROBLEM:
Write the Lewis structure for methanol (molecular formula CH4O), an important industrial alcohol that is being used as a gasoline alternative in car engines.

10. Multiple Bonds
If there are not enough electrons for the central atom to attain an octet, a multiple bond is present.
Step 5: If the central atom does not have a full octet, change a lone pair on a surrounding atom into another bonding pair to the central atom, thus forming a multiple bond.

11. Sample Problem 3
Writing Lewis Structures for Molecules with Multiple Bonds
PROBLEM:
Write Lewis structures for the following:
(a) Ethylene (C2H4), the most important reactant in the manufacture of polymers
(b) Nitrogen (N2), the most abundant atmospheric gas

12. Exceptions to the Octet Rule
Molecules with Electron-Deficient Atoms
B and Be are commonly electron-deficient.
Odd-Electron Species
A molecule with an odd number of electrons is called a free radical.

13. Exceptions to the Octet Rule
Expanded Valence Shells
An expanded valence shell is only possible for nonmetals from Period 3 or higher because these elements have available d orbitals.

14. Sample Problem 4
Writing Lewis Structures for Octet-Rule Exceptions
PROBLEM:
Write a Lewis structure and identify the octet-rule exception for (a) SClF5; (b) BFCl2.

15. Multiple Center Atom Molecules
How to draw and decipher

16. Figure 10.12
The tetrahedral shapes around the central atoms and the overall shapes of ethane (A) and ethanol (B).
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ethane
CH3CH3
ethanol
CH3CH2OH

17. Sample Problem 5
Predicting Molecular Shapes with More Than One Central Atom
PROBLEM:
Determine the shape around each of the central atoms in acetone, (CH3)2CO.

18. Molecular Shape and Molecular Polarity
Overall molecular polarity depends on both shape and bond polarity.
The polarity of a molecule is measured by its dipole moment (μ), which is given in the unit debye (D).
A molecule is polar if
it contains one or more polar bonds and
the individual bond dipoles do not cancel.

19. The orientation of polar molecules in an electric field.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Molecules become oriented when the field is turned on.
Molecules are randomly oriented.

20. Bond Polarity, Bond Angle, and Dipole Moment
Example: CO2
The DEN between C (EN = 2.5) and O (EN = 3.5) makes each C=O bond polar.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
CO2 is linear, the bond angle is 180°, and the individual bond polarities therefore cancel. The molecule has no net dipole moment (μ = 0 D).

21. Bond Polarity, Bond Angle, and Dipole Moment
Example: H2O
The DEN between H (EN = 2.1) and O (EN = 3.5) makes each H-O bond polar.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H2O has a V shaped geometry and the individual bond polarities do not cancel. This molecule has an overall molecular polarity. The O is partially negative while the H atoms are partially positive.

22. Bond Polarity, Bond Angle, and Dipole Moment
Molecules with the same shape may have different polarities.
CCl4
Bonds are polar, but individual bond polarities cancel.
CHCl3
Bond polarities do not cancel. This molecule is polar (μ = 1.01 D).

23. Sample Problem 7
Predicting the Polarity of Molecules
(a) Ammonia, NH3
(b) Boron trifluoride, BF3
(c) Carbonyl sulfide, COS (atom sequence SCO)
PROBLEM:
For each of the following use the molecular shape and EN values and trends to predict the direction of bond and molecular polarity, if present.

24. Finish up and complete the polarity section now!
Molecular Shapes Lab
Finish up and complete the polarity section now!

25. Draw the Lewis Structures for the following molecules
Determine the shape
CH3Cl
CH2O
BeCl2
BCl3
PF5
SF6
XeF4
SF4
ICl3

26. Lewis Structures for IonsK+
ClO2-1
CN-1
CO32-
SO42-

27. Exit Ticket Draw the Lewis Structure for CO2
Determine the shape and bond angles of CO2 according to the VSEPR theory.