Ions (Bohr Style)

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? • H = 1 • 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. 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. 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