Counting Atoms!Unit 3: Chemistry. Counting Atoms and Balancing Equations.

Elements e.g. H2, Pb, C, K

Compounds e.g. NaCl, KOH, H2O2

Chemical VocabularyUnit 3: Chemistry. Counting Atoms and Balancing Equations.

Chemical Vocabulary

Subscripts: Indicates how many atoms of a particular element are present

Coefficients: Indicates the total number ofcompounds/molecules present

Unit 3: Chemistry. Counting Atoms and Balancing Equations.

Counting Atoms1) List the different elements in each compound2) Count how many of that particular atom there

are.3) Total how many atoms there are in the

compound.

e.g. H2O

H (Hydrogen) 2 atomsO (Oxygen) 1 atom

Total: 3 atoms

Unit 3: Chemistry. Counting Atoms and Balancing Equations.

More Examples3 H2O2 (3 molecules of hydrogen peroxide)

H (Hydrogen) (2 atoms x 3 molecules) O (Oxygen) (2 atom x 3 molecules)

Total: 12 atoms

Pb (Lead) 1 atom N (Nitrogen) (1 atom x 2 molecules)O (Oxygen) (3 atom x 2 molecules) Total: 9 atoms

Pb(NO3)2

Unit 3: Chemistry. Counting Atoms and Balancing Equations.

How many atoms are in these compounds?KNO3

8 Cl2O

6 Ba(MnO4)2

Unit 3: Chemistry. Counting Atoms and Balancing Equations.

Counting Atoms

Unit 3: Chemistry. Counting Atoms and Balancing Equations.

Balancing Chemical Equations

Chemical EquationUnit 3: Chemistry. Counting Atoms and Balancing Equations.

• GOAL: There must be the same number of each atom on both sides of the equation.

REACTANTS = PRODUCTS(LAW OF CONSERVATION OF MASS)

Unit 3: Chemistry. Counting Atoms and Balancing Equations.

Balancing Equations

• Atoms cannot be created or destroyed by ordinary chemical means

• Reactants ALWAYS = Products

Unit 3: Chemistry. Counting Atoms and Balancing Equations.

Law of Conservation of Mass

Balancing Chemical Equationshttp://www.wikihow.com/Balance-Chemical-Equations

Unit 3: Chemistry. Counting Atoms and Balancing Equations.

• You can ONLY modify the coefficient #

• Balance H2 and O2 last

• If you have 3 hydrogen atoms on one side and 2 hydrogen atoms on another, try finding a common number between the two.

E.g.

_H2 + _N2 _NH3

H: 2 H : 3 (Unbalanced) H: 6 H : 6 (Balanced) - New Equation

3H2 + _N2 2 NH3

• Always double check your work by doing a final atoms count

Unit 3: Chemistry. Counting Atoms and Balancing Equations.

Tips when Balancing