1. Chemical Formulas and Equations
Mrs. Brostrom
Integrated Science

2. Chemical Formulas
A chemical formula is a shorthand way to use chemical symbols and numbers to represent a substance
Shows how many atoms of each kind are present in a molecule
methane (CH4), water (H2O), carbon dioxide (CO2)
Atom # C 1 H 4
Atom # H 2 O 1
Atom # C 1 O 2

3. A subscript is the number written below and to the right of the chemical symbol in a formula
If there is no subscript than only one atom of the element is present
Salt (NaCl), Magnesium chloride (MgCl2)
Atom # Na 1 Cl
Atom # Mg 1 Cl 2

4. Writing Formulas for Covalent Compounds
Composed of two nonmetals
The prefix tells you how many atoms of each element are in the formula
Prefix
# of Atoms
Mono- 1
Di- 2
Tri- 3
Tetra- 4
Penta- 5
Hexa- 6
Hepta- 7
Octa- 8
Nona- 9
Deca- 10

5. Writing Formulas for Ionic Compounds
Sodium chloride NaCl Na has a charge of 1+ Cl has a charge of 1- (1+) + (1-) = 0 Magnesium chloride MgCl2 Mg has a charge of 2+ (2+) + 2(1-) = 0
Contains a metal and a nonmetal
Make sure the compounds charge is 0 or the ion’s charges have cancelled out.
Add the suffix -ide to the nonmetal

6. Describing Reactions by Using Chemical Equations
A chemical equation uses symbols and formulas as a shortcut to describe a chemical reaction.
The starting materials in a chemical reaction are reactants.
The substances that are formed from the reaction are products.
C + O2CO2

7. Equations Must Be Balanced
Atoms are never lost or gained in a chemical reaction, they are just rearranged.
When writing a chemical equation, the number of atoms in the product must equal the atoms in the reactants.
The law of conservation of mass states that mass is neither created or destroyed in ordinary chemical and physical changes.

8. How to Balance an Equation
H2 + O2 H2O
To balance equations, you must use coefficients (a number that is placed in front of a chemical symbol or formula).
Count the atoms
Balance the O atoms
Balance the H atoms
2H2 + O2 2H2O
Atom
Reactant
Product H 2 O 1
Atom
Reactant
Product H 4 O 2

9. Balance the following equations
Na + Cl2NaCl
Mg + N2Mg3N2
Na + Cl NaCl
Atom
Reactant
Product Na Cl
Atom
Reactant
Product Mg N
Mg N2 Mg3N2
Atom
Reactant
Product Na Cl
Atom
Reactant
Product Mg N