1. Polyatomic Ions Ca(OH)2 Be(NO3)2 (NH4)2S
Polyatomic ions- a unit of more than one atom
Ways to identify polyatomic ions….
1. If you see elements in parentheses, these are the poly atomics
Ca(OH)2 Be(NO3)2 (NH4)2S
2. If you find the polyatomic ion on your polyatomic ions sheet!

2. Balancing Equations

3. 2CU + Zn(NO3)2  2CuNO3 + Zn REACTANTS PRODUCTS Coefficient Subscripts
YIELD SYMBOL
Coefficient
Subscripts
REACTANTS
PRODUCTS

4. Chemical Reaction Vocabulary
Chemical Reaction: One or more reactants change into one or more products
Reactant: A substance present at the start of a reaction
Product: A substance produced in a chemical reaction
Chemical Equation: An expression representing a chemical reaction; the formulas of the reactants (on the left) are connected by an arrow with the formulas for the products (on the right).
Example: Reactants Products

5. Law of Conservation of Mass
In a chemical reaction mass is conserved.
Mass cannot be created or destroyed
It can only change forms
Solid to liquid to gas
Change into another substance

6. Example
Before
After change
Which one has the greater mass?

7. Law of Conservation of Mass —Mass is never created or destroyed in a chemical reaction.
When material is burned, residue is less massive than original material
Ash, smoke, and gases escaped into the air—(they are still considered matter.)
Their mass was not lost, only relocated due to the law of conservation of mass.

8. Law of Conservation of Mass
We learned how to count atoms in a chemical formula,
now we have to make sure we have the same amount of atoms on each side of the reaction.

9. Balancing Chemical Equations
A chemical equation in which mass is conserved; each side of the equation has the same number of atoms of each element
Is this equation balanced?
Fe + O Fe2O2
How many….on the reactants side? On the products side
Fe Fe
O O
The iron is not balanced to conserve mass. We have 1 on the left and 2 on the right, so we need to at a coefficient (small whole number that are placed in front of the formulas in an equation in order to balance it). So the equation would look like this:
2Fe + O Fe2O2

10. Balancing Steps
1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients as needed to make #s equal on both sides of the equation. Coefficient  subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!!

11. Helpful Tips Balance one element at a time.
Update ALL atom counts after adding a coefficient.
If an element appears more than once per side, balance it last.
Balance polyatomic ions as single units.
Common poly atomics: SO4,PO4,CO3,OH
Example: “1 SO4” instead of “1 S” and “4 O”