1. Ions (Bohr Style)

2. How to make an Ion Add or subtract electrons Add electrons = anion (-)
Subtract electrons = cation (+)
Check it out!

3. Making an Anion
O2- +8 O
-10

4. Making a Cation
Na+
+11 Na
-10

5. Mg

6. N

7. F

8. H

9. Steps for Lewis Structures of Molecules
Chemistry

10. Step 1: How Many Bonds Does Each Element typically Make?
F (halogens) = 1
O (S) = 2
N (P) = 3
C (Si) = 4

11. Step 2: Decide Which Atom Goes in the Middle
Which element in the compound has the fewest atoms?
Which element makes the most bonds?
Put that one in the middle!
Remember: Hydrogen and Halogens will NOT be in the middle
CO2 Which will you put in the middle?

12. Step 3: Arrange Other Atoms around the Central Atom with Valence Electrons
Use symmetry to place other atoms
Draw valence electrons for each atom
Anticipate possible bonds O C O

13. Step 4: Follow the Octet Rule for Each Atom
Pair up unpaired electrons
Double check that each atom has 8 electrons
Unless it’s Hydrogen
Each atom gets to count the shared electrons O C O

14. Step 5: Make Each Shared Pair a Covalent Bond
Draw a line through each shared pair
Each shared pair is two electrons
Remember:between two atoms, one shared pair is a single bond, two shared pairs are a double bond, three are a triple bond O C O

15. O C O Step 6: Check Make sure each atom has an octet (except Hydrogen)
Does each atom have the predicted number of bonds?
Check total number of electrons O C O

16. O C O Step 7: Make it Pretty Make sure bonds are between atoms
Distribute electron pairs symmetrically O C O

17. Try it!
H2O
CH4
NF3
SiO2
OCl2