1. Welcome Back!!! 

2. Drill What is the chemical formula when the following combine:
Mg and O
Al and Cl
**Think criss-cross method! 
Drill

3. Information
Polyatomic Ions
Criss-Cross Practice
Reverse Criss-Cross
Exit Slip
Agenda

4. Determine the formula when given a polyatomic ion and another cation/anion
Determine the charge on a metal when given a formula
I Can…

5. Unit 3 Tests Grades are Updated on BCPSOne
If you want to do a redo – best time is to do it right before break!
Unit 3 Tests

6. Please Note If you were absent, best to take the test before break
This information is going to be important to know as we continue in this class
If you are confused, PLEASE see me ASAP to make sure you have an understanding!!!!
Please Note

7. Charged molecules that contain two or more atoms covalently bonded.
They are bounded very tightly together, so the ion retains its identity within an ionic compounds and over the course of many chemical reactions
Polyatomic Ions

8. Hydroxide- OH-
Why a Charge?

9. Do I have to Memorize them??
Yes and No
You will be given a small list and then will have to determine the others
Do I have to Memorize them??

10. Criss-Crossing with Polyatomic Ions
Polyatomic ions DO NOT break apart when writing a chemical formula
Criss-Crossing with Polyatomic Ions

11. Criss-Crossing with Polyatomic Ions
If you have more than one polyatomic ion in the formula, you MUST put parentheses around it to show there are more than one of the polyatomic ions
If there is only 1 atom, you DO NOT need to include parentheses around it
Criss-Crossing with Polyatomic Ions

12. DO NOT DO
Examples
(Na)2(CO3)
MgOH2
(NH4)(OH)
Na2CO3
Mg(OH)2
NH4OH

13. Li and SO4-2
Al and CO3-2
NH4+ and PO4-3
Examples

14. Able to tell what charge metals have since some transition metals have different charges
Example
Reverse Criss Cross

15. Determining how many Atoms
If you have parentheses, you must multiple the numbers together
Determining how many Atoms

16. Exit Slip What is the chemical formula when Sr and OH combine?
What is the chemical formula when NH4 and PO4 combine?
What is the charge on the metal: Pb(CO2)2
How many oxygen atoms are in Al(NO3)3
Exit Slip