1. What shape are your molecules in?
VSEPR
What shape are your molecules in?

2. Background you need… Lewis structures Bonding (covalent)
Lewis structures
How many bonds do each element make?
What can expand?
Bonding (covalent)
Polarity
Electronegativity and determining bond type
Resonance v. Isomers
Formal charge
Let’s review now…..

3. Lewis Structures
Remember that Lewis structures want a full outer shell
Remember that for a given Lewis structure, the number of electrons around the atoms must equal the total number of electrons individually assigned.
Ex: C has 4, H has 1, so CH4 must have 8 total

4. Resonance Structures
Have the same alignment of atoms, but different bonding (electrons ONLY are moved, both in bonds and lone pairs)

5. Determining formal charge
Formal charge can be determined by:
Normal number of electrons in outer shell -
[(1/2 the number of bonded electrons) +
lone electrons]
_____________________________________
= formal charge
Example: N in NH4
FC =5- [(1/2 of 8)+ 0]= +1

6. Formal charge and stability
The most “happy” molecules tend to have no formal charges
However, molecules may be “happy” if they have not NET charge on them (if there is 1+ and 1-, so a net of +1 + (-1)=0)
Resonance structures that are the best have a minimal formal charge and a full octet around each atom

7. What is VSEPR?
Valence
Shell
Electron
Pair
Repulsion
Theory

8. Why? The shape of molecules influences their characteristics:
The shape of molecules influences their characteristics:
Things like polarity which influence things like
boiling point, melting point, which dictate their nature (solid, liquid or gas at room temperature)

9. The parent geometries: all others come from these

10. Linear
AX2

11. Trigonal planar
AX3

12. Tetrahedral
AX4

13. Pyramidal (Trigonal or tetrahedral)
Tetrahedral parent shape
1 lone pair of electrons
AX3E

14. Bent
Tetrahedral parent shape
2 lone pair of electrons
AX2E2

15. When determining polarity it is important to look at the dipole moments- do they cancel out?