1. Valence Shell Electron Pair Repulsion Theory
Planar triangular
Valence Shell Electron Pair Repulsion Theory
Tetrahedral
Trigonal bipyramidal
Octahedral

2. VSEPR Click in this box to enter notes.
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3. Molecular Structure
Molecular structure – the three-dimensional arrangement of atoms in a molecule

4. VSEPR Theory
VSEPR Theory (Valence Shell Electron Pair Repulsion Theory)
A model for describing the shapes of molecules whose main postulate is that the structure around a given atom is determined by minimizing the electron pair repulsion
Therefore, the electrons and elements bonded to the central atom want to be as far apart as possible

5. VSEPR Theory
Based on Lewis structures we can know the shape or “geometry” of molecules
The theory that predicts geometry (based on Lewis structures) is abbreviated VSEPR
VSEPR (pronounced “vesper”) stands for Valence Shell Electron Pair Repulsion
VSEPR, as the name suggests, predicts geometry based on the repulsion of electron pairs (in bonds or by themselves)
Electrons around the central nucleus repel each other. Thus, resulting structures have atoms maximally spread out (balloon demo)

6. VSEPR overview
The balloons represent electron clouds. At the end of each balloon will be a peripheral atom. The balloons meet at a central atom.
Each shape containing 2-6 peripheral atoms has a name (you will have to know these)
Sometimes the molecules are represented by AXY, where Y is the # of peripheral atoms
AX2 = linear
AX3 = planar triangular
AX4 = tetrahedral (tetra = 4 faces)
AX5 = trigonal bipyramidal (2 pyramids)
AX6 = octahedral (octa = 8 faces)
Work on handout (follow instructions on sheet)

7. VSEPR Steps Draw the Lewis structure for the molecule
Count the total number of things that are around the central atom to determine the electron pair geometry
Imagine that the lone pairs of electrons are invisible and describe the molecular shape

8. SORRY…
Yes…you must memorize the main shapes and bond angles

10. 2 Electron Pairs
If there are 2 things attached to the central atom, the shape is linear
Bond angle = 180°

11. VSEPR: Two Electron Pair
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12. 3 Electron Pairs
If there are 3 electron pairs the shape will be trigonal planar
Bond angle = 120°

13. VSEPR: Lone Pairs

14. Lone pairs
Thus far we have considered (built) only structures where there are no free electrons around the central atom H C H C
Vs. H N H N or or
These electrons that are not involved in bonds are called “lone pairs”
Essentially, they have the same influence on molecular structure as electron pairs in bonds
The result is some weird shapes and names…

15. 3 electron pairs
Now imagine that you have 3 electron pairs, but one is just a lone pair (invisible) what would it look like then?

16. VSEPR: Three Electron Pair
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17. 4 electron pairs
If there are 4 electron pairs, the shape will be tetrahedral
Bond angle = 109.5°

18. Variations on Tetrahedral Molecule
The tetrahedral molecule is AX4
Lone pairs can be indicated with AXYEZ, where Z is the number of lone pairs
By replacing 1 bond with a lone pair the tetrahedral shape becomes “trigonal pyramidal”
AX3E
By replacing two bonds with lone pairs we get a “bent” (non-linear) shape (AX2E2 )

19. 4 electron pairs
What if 1 of the electron pairs is a lone pair (invisible)? What would it look like then?
Trigonal Pyramidal

20. 4 electron pairs
What if there are 2 lone pairs (invisible)? What would it look like then?
bent

21. VSEPR: Four Electron Pair
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22. 5 electron pairs
If there are 5 electron pairs the shape will be Trigonal Bipyramidal
Bond angles = 90º & 120º

23. Variations on Trigonal Bipyramidal
AX5 is trigonal bipyramidal
AX4E is unsymmetrical tetrahedron
AX2E3 is linear
AX3E2 is T-shaped

24. 5 electron pairs
What is there is 1 lone pair (invisible)
Seesaw

25. 5 electron pairs
What is there are 2 lone pairs (invisible)
T-shaped

26. VSEPR: Iodine Pentaflouride
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27. Variations on Octahedral Shape
AX6 is octahedral
AX5E is square pyramidal
AX4E2 is square planar
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29. All VSEPR shapes are based upon certain hybrids.
sp2 hybrids make bent, trigonal planar.
sp3 hybrids make water bent, trigonal pyramidal, and tetrahedral.

30. Bonding in H2 Click in this box to enter notes.
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31. Hybridization: sp Click in this box to enter notes.
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32. Hybridization: sp2 Click in this box to enter notes.
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33. Hybridization: sp3 Click in this box to enter notes.
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34. Resonance – molecular structures are actually the average of all equivalent structures of a molecule.
Bond length -
Single>double>triple