1. Chapter Seven Molecular Geometry & Bonding Themes

2. Section 7.1 Molecular Geometry

3. What is molecular geometry?
Shapes of molecules (molecules actually have 3D structures that affect how they bond in reactions)
Based on electrons and their repulsion from each other
Valence Shell Electron Pair Repulsion (VSEPR)
Focused on general model ABx
A = central atom, B = terminal (attached) atoms

4. Electron Domains & VSEPR
Recall: Electron Pairs can be bonding pairs or lone pairs
Bonding pairs may be single bonds or multiple bonds
An electron domain is a lone pair or a bonded pair
(double and triple bonds only count for ONE electron domain)

5. Electron Domains & VSEPR
How many electron domains do these molecules have?

6. Electron Domain Geometry
Geometric shapes based on electron domains
AB2
Linear
180° (provided no lone pairs on central)
Ex: CO2
AB3
Trigonal Planar
120° (provided no lone pairs on central)
Ex: BF3

7. Electron Domain Geometry
Geometric shapes based on electron domains
AB4
Tetrahedral
109.5° (provided no lone pairs on central)
Ex: CH4
AB5
Trigonal Bipyramidal
120° (equatorial atoms) & 90° (axial atoms)
Ex: PCl5

8. Electron Domain Geometry
Geometric shapes based on electron domains
AB6
Octahedral
90° between all atoms (provided no lone pairs on central)
Ex: SF6

9. Drawing 3D structures on paper
It is helpful to draw molecules on paper with 3-Dimensionality to better visualize the shape

10. Visualizing it!

11. Electron Domain Geometry vs. Molecular Geometry
Electron Domain: based on electron domains (bonded and unbonded)
Basically, it looks at ALL the electrons
Molecular Geometry: based on atoms ONLY (bonded pairs only)
Basically only looks at electrons in bonds (or atoms)

12. Steps for determining geometry
Draw Lewis Structure
Count electron domains around central atom
Determine Electron Domain Geometry
Determine Molecular Geometry from atoms only

13. Electron Domain Geometry vs. Molecular Geometry
Consider the following three compounds:
CH4, NH3, H2O
What are their electron domain geometries?
What are their molecular geometries?

14. Practice
Determine what the electron domain geometry and molecular geometry are for the following compounds:
SO2
XeF4

15. Geometry with lone pairs
Some electron domains repel MORE than others
Lone pairs repel more
Because not bonded, they experience less nuclear attraction
Double and Triple bonds repel more
Due to higher electron density

16. Geometry with lone pairs

17. Geometry with lone pairs
Other examples

18. Practice
Determine the electron domain geometry and the molecular geometry for the following. Include bond angles as well.
SeO2
SF6

19. Group Quiz #1
State the electron domain geometry, the molecular geometry and the bond angle (if the bond angle is not ideal, state “less than _____°”)
PCl3
SeCl4

20. Molecules with Multiple Central Atoms
A central atom is one where it is surrounded by 2 or more atoms
Determine the multiple shapes in the molecule around each central atom
Ex:

21. Section 7.2 Molecular Geometry & Polarity

22. Recalling Polarity
Recall: A bond between 2 atoms is polar covalent when difference in electronegativity is greater than 0.5
A molecule OVERALL can also be polar or nonpolar
Based on geometry of molecule and
Individual bonds in molecule

23. Some simple examples
CO2 and H2O

24. How to check if molecule is polar
First, check if there are lone pairs of electrons
If yes, it is POLAR (unless they are “balanced”)
If no lone pairs, check if there are polar bonds
If there are no polar bonds, is is NON POLAR
If there are polar bonds, check for symmetry
If all terminal atoms are the same, it is NON POLAR
If terminal atoms are not the same, but there is symmetry, it is NON POLAR
If terminal atoms are not the same, and there is no symmetry, it is POLAR

25. Some Examples

26. Practice Determine if the molecule is POLAR or NON POLAR CH2Cl2 & XeF4
For each hypothetical molecule below, draw one structure that is polar and one that is non polar
H2SF4 & H2PCl3

27. Group Quiz #2 For each molecule below, determine SbCl5 I3-
the electron domain geometry,
the molecular geometry,
draw the 3D-structure on paper,
state if it is polar or nonpolar
SbCl5
I3-

28. Section 7.3 Valence Bond Theory

29. Valence Bond Theory
Definition: atoms share electrons when an atomic orbital on one atom overlaps with an atomic orbital on the other

30. Valence Bond Theory Explains why atoms share electrons
Potential energy of resulting molecule is lower than combined energies of isolated atoms
A.K.A. when bonds form, energy given off
Therefore, energy required to break bonds

31. Section 7.4 Hybridization of Atomic Orbitals

32. Hybridization Consider BeCl2 How can it bond with 2 atoms???
Hybridization: mixing of atomic orbitals

33. Hybridization
Hybrid orbitals are always shown in GREEN

34. Hybridization
Consider BF3

35. Hybridization
Consider CH4

36. Hybridization
Consider PCl5

37. Hybridization
Consider SF6

38. Steps for Hybridization
Draw Lewis Structure
Count # of electron domains (this is # of hybrid orbitals needed)
Determine the hybrid orbital needed
Draw ground state configuration of central atom
Place electrons in the hybrid orbitals one at a time

39. Examples
Use hybrid orbital theory to explain the bonding in BrF5

40. Group Quiz #3
Show the hybridization of the following molecule. Be sure to include a) what type of hybrid orbital is needed and 2) the orbital diagram of the hybrid orbital
XeF4

41. Section 7.5 Hybridization in Molecules Containing Multiple Bonds

42. Hybridization with Multiple Bonds
How many electron domains around the carbons?
What hybrid orbitals are needed?

43. Hybridization with Multiple Bonds
Bonds that are made using hybrid orbitals (or along the internuclear axis) are called sigma (σ) bonds
Bonds that are made using remaining p orbitals and overlap on the sides are called pi (π) bonds

44. Hybridization with Multiple Bonds

45. Hybridization with Multiple Bonds