1. Shapes of Molecules and Ions with 5 and 6 negative centers Section 14.1

2. Sulfur Hexafluoride Octahedral with bond angles of 90º and 180º Notice there are 12 electrons around the sulfur atom

3. VSEPR Theory Can be used for 5 and 6 negative centers Elements in the 3 rd and lower periods of the p-block can promote one or more electrons from a filled s or p orbital to an unfilled, low energy d orbital More unpaired electrons are available for bonding

4. Continued Have an expanded valence shell with more than 8 electrons Usually occurs when the atoms are relatively small and very electronegative so they can fit around the central atom Lewis structures are a little more challenging as you have to consider the total number of electrons available Examples: SF 6, PCl 5, XeF 4, PF 6 -

5. Phosphorus Pentachloride Trigonal bipyramidal with angles of 90º and 120º

6. Xenon Tetrafluoride Unshared (lone) pairs of electrons distort the shape to make it a square planar with bond angles of 90º

7. Sulfur Hexafluoride Shape is an octahedron See pages 107 or 375 for additional pictures and examples

8. Resonance Structures Consider the nitrate ion and its Lewis structure It has three possible structures Note the use of lines and dots whereas you must use one or the other

9. Continued Experiments have shown that the bonds do not really switch back and forth Instead, all the bonds have the same length and energy A better structure is called a resonance hybrid:

10. Continued The shape is trigonal planar The electrons are said to be delocalized as in they are shared evenly and not with just one nucleus Consider the nitrite ion. The resonance structures are:

11. More on the Nitrite Ion The shape is bent The resonance hybrid is:

12. Consider the Carbonate Ion Has three resonance structures The resonance hybrid is trigonal planar

13. Ozone (O 3 ) Has two resonance structures The resonance hybrid is bent

14. RCOO - R represents a combination of CH 3 with a number of CH 2 attached (or not) The important part is that the two oxygens experience resonance The shape is trigonal planar

15. Benzene Ring The resonance structures are called Kelule structures Resonance structures can be drawn as any of the examples below