1. Do Now: Re-arrange the following rules in the correct order:
When finished complete pgs
Give any leftover electrons to the central atom.
If the species is charged, draw square brackets around it with the charge as a super-script.
Arrange the atoms so the least electro-negative atom is in the centre. Hydrogen is always on the outside, as is fluorine.
Add-up the total number of valence shell electrons in the species. Add an electron for each negative charge and subtract one for each positive charge.
Give each outer atom a full valence shell of electrons. This is usually 8 electrons, but would be 2 for Hydrogen.

2. Shapes
Y12 Chemistry

3. Shapes of Molecules
The shapes of molecules are determined by the way clouds of electrons are arranged around the central atom in the molecule.
Since clouds of electrons are negatively-charged, they repel each other. e- e-

4. O S Electron clouds Electron clouds can be bonding or non-bonding
Non-bonding electron clouds O S
Bonding electron clouds

5. Linear One electron cloud
A molecule containing only a single cloud of electrons must be linear.
Bond angle = 180o

6. Linear Linear Two electron clouds Bond angle = 180o One lone pair
No lone pairs
Linear

7. Linear Bent Three electron clouds Trigonal planar Bond angle = 120o
two lone pairs
Linear
one lone pair
Bent
no lone pairs
Trigonal planar

8. Four electron clouds Linear Bent Tetrahedral Bond angle = 109o
Three lone pairs
Two
lone pairs
Linear
Bent
No lone pairs
One lone pairs
Trigonal pyramidal
Tetrahedral

9. Drawing Tetrahedral and Trigonal Pyramids
Both of these have bonds that, if put onto a piece of paper, would not sit flat.
They need to be drawn differently.
bonds in the plane of the page are drawn as sticks/lines
bonds coming toward you (out of the page) are drawn as a wedge
bonds going away from you (behind the page) are drawn as a dashed wedge).