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!

Balancing Equations

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

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

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

Example Before After change Which one has the greater mass?

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.

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.

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 + O2 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 + O2 Fe2O2

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!!!

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”