1. Formal Charge

2. Formal Charge It is a way to predict what structure is most likely.
# of valence e- in atom minus # of e- assigned to it in the molecule

3. Formal Charge Lone pairs count individually Bond pairs count as half
=(# of val e- in atom) - ((# of e- in lone pair) +1/2(# of e- in bond pairs))

4. Formal Charge Ex: Which one is the most plausible structure?
:S=C=S: or :C=S=S:
Val e
e pic FC .. .. .. ..

5. Formal Charge Plausible? Usually the one with no formal charge.
If required, they should be the smallest possible charges, and negative should appear on the most electronegative element.
Adjacent atoms should not carry a formal charge of the same sign.
Total formal charge must be zero for a neutral molecule and equal to the charge of an ion.
So……?

6. Formal Charge Ex: Which one is the most plausible structure?
::S=C=S:: or ::C=S=S::
Val e E’ FC

7. F P O O P F
Val e
e pic FC

8. Lewis structures, shapes, angles, hybridization
BONDING
Lewis structures, shapes, angles, hybridization

9. LEWIS STRUCTURES COVALENT compounds Elements share electrons
A line represents TWO shared electrons
OCTET rule
Every element wants at least 8 electrons (EXCEPT hydrogen and helium ~ they only want 2)
Other exceptions ~ Be only wants 4, B only wants 6
Some can have an EXPANDED octet (only 3rd energy level and below since the extra electrons go in d orbitals)

10. STEPS FOR LEWIS STRUCTURES
Draw the atoms
The central atom goes in the middle, and the others go around it
The central atom is usually the one you have the LEAST of (or the least ELECTRONEGATIVE if you only have one of two or more elements)
Count your total number of valence electrons
Use your periodic table to add up the number of valence electrons in the formula

11. STEPS FOR LEWIS STRUCTURES
BOND
Everything must be bonded to the central atom
Fix OUTER atoms
Every outer atom must have 8 electrons (or 2 if it is hydrogen)
Fix CENTRAL atom
Extras = LONE PAIR(S)
If your count is ZERO and the central atom still does not have 8, then you need a MULTIPLE BOND

12. A COUPLE EXAMPLES
CH4
NF3

13. A COUPLE EXAMPLES
CO2
SiO32-