ABxEy
Notation
How can geometric
structure in 3d be
predicted given the
numbers of valence
electrons?
A represents central atom
B represents surrounding atoms
E represents unshared pairs of
valence electrons on CA
x and y - subscripts that represent
number of surrounding atoms (B)
and
number of unshared pairs of
valence electrons (E)on CA
Example: Water
H2O
Oxygen CA
Hydrogen surrounding atoms
2 surrounding atoms
2 pairs of unshared valence electrons
Notation for ABxEy would be:
CO2
CH4
NH3
PCl5
SF6
BF3
BrF5
IF4
Answer: AB2 E2
YOUR TURN…
C N O P S may have multiple
bonds… double or triple
Rare for Cl
Get VSEPR from ABxEy
notation
How many groups of e-?
X + Y= total groups of v eTHIS determines shape of
molecule
What are the shapes of molecules ?
How is geometry predicted?
RESONANCE
Multiple bonds
Deficient
Extended
Odd number of v e-
Resonance
Double bond or other may
occur
Anywhere on diagram
Can flip in nature
May move valence e- and flip
bond !
Where it is, averages out