Ions (Bohr Style)

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

Making an Anion O2- +8 O -10

Making a Cation Na+ +11 Na -10

Mg

N

F

H

Steps for Lewis Structures of Molecules Chemistry

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

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?

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

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

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

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

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

Try it! H2O CH4 NF3 SiO2 OCl2