1. 2/10/16 Today I will determine the shapes of small molecules.
Warm Up –
Draw the Lewis Structure for CO3-2

2. Chapter 8 – Molecular Shape
Chemistry

3. Structural Formulas
1. Count up the total number of valence electrons present.
2. Put the element with the lowest electronegativity in the center.
3. Add lone pairs to outside, then inside elements to make an octet.
4. Count up the total number of electrons drawn on! If it equals the total valence number, you are done!
5. If you have used too many electrons, create double or triple bonds, by removing two pairs and creating one more bond….then recount!

4. Structural Formulas Cl Cl B Cl Exceptions to the Octet Rule! BCl3
Atoms with less than an octet
Beryllium is happy with 4 electrons!
Boron is happy with 6 electrons!
BCl3
You need to recognize that B and Be are fine with less than 8 electrons! Cl
B  3
x 1
= v.e.
Cl  7
x 3
= 21 v.e. Cl B Cl
= 24 v.e.

5. Structural Formulas F Be F Exceptions to the Octet Rule! BeF2
Atoms with less than an octet
Beryllium is happy with 4 electrons!
Boron is happy with 6 electrons!
BeF2
Be  2
x 1
= v.e.
F  7
x 2
= 14 v.e. F Be F
= 16 v.e.

6. Molecular Geometry
Structural Formulas explain what atoms are bonded where, but they only show us an atom in two dimensions.
Molecular Geometry – shows us an atom in three dimensions!

7. Molecular Geometry
Ball and Stick models – three dimensional physical model of molecular shape.

8. Molecular Geometry Why do atoms arrange in different shapes?
Electrons of the outer atoms want to get as far away from one another as possible.
Like charges repel!

9. Molecular Geometry Valence Shell Electron Pair Repulsion Theory
VSEPR Theory
In a small molecule, the pairs of valence electrons are arranged as far apart from each other as possible.
VSEPR is concerned with both bonded electron pairs (bonds) and unbonded pairs (lone pairs).

10. Molecular Geometry
1. Draw the structural Formula 2. Determine the Base Geometry by counting the number of substituents 3. Determine the Shape by looking at the number of unbonded pairs *Substituent – an atom or unbonded pair attached to the central atom.

11. Molecular Geometry – Linear Base Geometry
Substi-tuents
Lone pairs
Base
(Electron)Geometry
Shape
Shape Name
Examples
Bond Angle 1
0-3
Linear
HF, O2
180° 2
BeCl2, CO2
*Any molecule that only has two atoms, must be linear, regardless of unbonded pairs!

12. Molecular Geometry – Trigonal Planar Base Geometry
Substi-tuents
Lone pairs
Base (Electron) Geometry
Shape
Shape Name
Examples
Bond Angle 3
Trigonal Planar
BF3, CO3-2
120° 1
Bent
NO2-, O3
<120°

13. Molecular Geometry - Tetrahedral
Substi-tuents
Lone pairs
Base (Electron) Geometry
Shape
Shape Name
Example
Bond Angle 4
Tetrahedral
CH4, PO4-3
109.5° 1
Trigonal Pyramidal
NH3, PCl3
<109.5° 2
Bent - 105
H2O

14. Homework
VSEPR Theory #1 – Find base geometry, and shape for each. Predict bond angles.

15. 2/11/16 Today I will practice VSEPR
Warm Up – What is the shape of PBr3?

16. Expanded Octets
Less than octet – He, B, Be
More than an octet

17. Geometry – Trigonal Bipyramidal
Substi-tuents
Lone pairs
Base (Electron) Geometry
Shape
Shape Name
Example
Bond Angle 5
Trigonal Bipyramidal
PCl5
120°, 90° 1
See Saw
SF4
180° 2
T-shaped
ClF3
90°, 180° 3
Linear
XeF2

18. Molecular Geometry - Octahedral
Substi-tuents
Lone pairs
Base (Electron) Geometry
Shape
Shape Name
Example
Bond Angle 6
Octahedral
SF6
90° 1
Square Pyramidal
ClF5
<90° 2
Square Planar
XeF4

19. Expanded Octets

20. 2/12/16 Today I will demonstrate molecular shape
Warm Up – What is an expanded octet?

21. 2/16/16 Today I will demonstrate molecular shape
Warm Up – Describe the method of finding shape.

22. 2/17/16 Today I will demonstrate molecular shape
Warm Up – Describe the method of finding shape.

23. 2/18/16 Today I will demonstrate molecular shape
Warm Up – What is the base geometry and shape of NCl3

24. 2/19/16 Today I will describe hybridization and bond length.
Warm Up – What is the shape of ClO3-1?

25. Hybrid Orbitals
Another theory of molecular geometry is hybridization of orbitals
Hybrid Orbitals – combinations of atomic orbitals

26. Bond Length
Different pairs of atoms actually form bonds of different length.
Moving down a group, bond length increases
Cl---Cl > F---F (larger atoms)
Single bonds > Double bonds > Triple bonds
C---O > C==O

27. Drawing Ball & Stick Models

28. 8.1 Review & Reinforcement
Don’t do # 16 or 17

29. 2/22/16 Today I will draw molecular polarity
Warm Up – What is the base geometry, shape and hybridization of CO2?

30. Polarity
Polarity
1. Bond Polarity
2. Molecule Polarity

31. Polar Bonds Covalent Bonds can show polarity
Polarity – unequal sharing of electrons
Partial positive
Partial negative
F is more electronegative than C, which means it has a greater pull on the electrons in the bond.
Therefore, the electrons are unbalanced toward the F.

32. Electronegativities of Representative Elements
Polar Bonds
Electronegativities of Representative Elements
Fluorine
4.0
Oxygen
3.5
Chlorine
3.0
Nitrogen
Bromine
2.8
Carbon
2.5
Sulfur
Hydrogen
2.1
Phosphorus
Boron
2.0
Silicon
1.8
Significant Electronegativity Difference
If the difference is ≤ 0.4, the bond is non-polar.
If the difference is > 0.4, the bond is polar
Are the following bonds polar or nonpolar?
C-C
N-O
H-P
C=O

33. Polar Molecules Molecules can be polar or non-polar too.
Dipole – a molecule with a positive end and a negative end (polar) HF
Draw in the dipole arrow. Points toward negative
HF only has a polar bond.

34. Polar Molecules
HF was easy to figure out because it was only two atoms.
What about CO2?
CO2 is composed of two polar bonds, but tests show that it is a nonpolar molecule.
HOW?

35. Polar Molecule
In order to determine polarity, you must look at both the bond polarity and the shape of the molecule!
Polar molecules will have a NET DIPOLE
Where is the center of the positive ends?
Where is the center of the negative ends?
If there is a separation, draw in a net dipole arrow.
CO2 is nonpolar!
What shape is CO2?
Linear

36. Polar Molecules H2O Where is the center of the positive ends?
Where is the center of the negative ends?
If there is a separation, draw in a net dipole (toward negative)
H2O is polar!
What shape is H2O?
Bent - 105

37. Polar Molecules
Typically, if the molecule is symmetrical, it will be non-polar and if the molecule is asymmetrical, it will be polar (as long as the substituents are the same!)
Which shapes could be symmetrical?

38. Polar Molecules H2CO Where is the center of the positive ends?
Where is the center of the negative ends?
If there is a separation, draw in a net dipole (toward negative)
H2CO is polar!
What shape?
Triangular Planar

39. Polar Molecules
Polarity determined by both shape and the polarity of bonds.
Look at H2S

40. Homework
Polar Bonds and Molecules WS

41. 2/23/16 Today I will review polarity
Warm Up – Describe how we determine if a molecule is polar or non-polar.

42. 2/24/16 Today I will describe intermolecular forces
Warm Up – Draw the ball and stick model of water and show the molecular polarity

43. Polar Molecules One of the most important molecules on earth is water.
Water only has the properties it does because it is polar!
Liquid at room temperature
Life on Earth might not be possible if water were non-polar!

44. Intermolecular Forces
Intermolecular forces – a force of attraction that exists between neighboring molecules because of their polarity
Dipole-dipole
Attraction between neighboring dipoles
Molecules align in an electrical field

45. Intermolecular Forces
Hydrogen bond – strong dipole bond between the hydrogen atom of a molecule and a highly electronegative atom of another molecule such as F, O or N.
Especially useful in water – keeps water a liquid

46. Large Molecules Small molecules – Shape helps determine polarity
Large molecules – Polarity helps determine shape!

47. Homework 8-2 R & R Don’t do #12
Do #’s 7-11 on the back, or a separate sheet
Assume the B-I bond in #13a is non-polar

48. 2/25/16 Today I will review ch 8 Warm Up – Find the following for CS2
base geometry,
shape,
hybridizations,
draw the ball and stick model,
bond polarity,
molecule polarity (draw in net dipole if there is one)

49. 2/26/16 Today I will review chapter 8
Warm Up – Describe the process of determining whether a molecule is polar or nonpolar from the very beginning.