1. Shapes of molecules and ion
Recall expanded octets
Determine the shape of molecules

2. Starter
Ncea question 06,07,08 Lewis diagrams

3. Recall Incomplete octet Due to insufficient pairs of electrons
Occurs when central atom is
Examples so far BF3,AlCl3,BeCl2
examples BH3, NO,

4. Recall Expanded octet Atoms belonging to th 3rd period or lower
Use the empty 3d ( level 3 can hold up to 18 electron using 3s, 3p and 3d as the valence shell) this is the case with sulphur and phosphorus
Examples ozone, PF5 PCl5 SCl6, SF6, BrF3 and BrF5

5. Ions Monatomic ion – single atom
Polyatomic – contain more than one atom eg ammonium ion, nitrate ion, carbonate and sulphate ion.
Drawing Lewis structures adjust the valence number of electrons according to the charge on the ion
Square brackets are place around the structure and the charge place on the outside.

6. Note: Dative Bond
This is when both electrons in a covalent bond are supplied by one atom
An arrow can drawn to show the direction that the electrons have been donated (donor > acceptor)
If the central atom doesn't have an octet of electrons an outer atom may provide both electrons to be shared between them.
If the central atom has a lone pair of electrons it may provide both for the shared bond
Example ammonium ion, nitrogen dioxide.

7. Limitations of Lewis structures
Sometimes there is more than one structure for a molecule or polyatomic ion other than the expected one
These have been found through X-ray diffraction work
Examples sulphate ion, phosphate ion and the chlorate ion

8. Shapes
Lewis structure predict shapes of molecules and ions as they show sets of electrons bonding and non bonding around the central atom
Each bond – area of electron density that arrange themselves due to electron repulsion VSEPR valance shell electron pair repulsion theory

9. Shapes of Molecules
Molecules (covalent chemicals) form certain shapes depending on how many lone and bonding pairs of electrons it has.
Because the electron pairs repel each other we get certain shapes being formed. These are due to a certain rule called VSEPR (Valence Shell Electron Pair Repulsion)
Bonding pair – these can also be drawn as straight lines
Lone pair

10. Shape Depends on number of atoms linked to the central atom
Number of regions of electron density
Lone pairs are not drawn in the final shape
The name of the shape is determined by the bonded atoms only
We can also find bond angle using Lewis diagram and shape

11. Trigonal Planar (Flat)
VSEPR – base shapes 2
Electron Repulsion
Zones 3 4 5 6
Shape:
Linear
Trigonal Planar (Flat)
Tetrahedral
Trigonal Bipyramid
Octahedral

12. 3D Shapes Shape Examples Formula Lewis Diagram Tetrahedral CH4
Trigonal Pyramid
NH3
Bent/Angular
H2O

13. “Flat” Shapes Shape Examples Formula Lewis Diagram Linear CO2
Trigonal Planar
CH2O

14. Level 3 - Shapes Shape Examples Formula Lewis Diagram Octahedral SCl6
Trigonal Bipyramid
PCl5
Square Planar
XeF4

15. Worksheet and models
Complete worksheet with example
Make straw models