Download Formula Notes and Criss Cross Method Guided

Formulas
 Combining symbols of different elements in a compound is called a
CHEMICAL FORMULA.
 Examples:
Na and Cl = NaCl (salt)
H and Cl = HCl (hydrochloric acid/stomach acid)
Fe and S = Fe2S3 (Iron sulfide)
C and O = CO2 (Carbon dioxide)
O3 = Ozone
What is the chemical formula for water? _______________________
 Subscripts
1. Written below and after the symbol of the atom to indicate
the number of atoms of that element in the compound.
2. If no subscript then = 1 atom
3. Example: H2O 2 Hydrogen atoms and 1 oxygen atom in
one molecule of water.
4. Fe2S3
How many iron atoms? _____________
How many sulfur atoms? ____________
What is the ratio of the carbon atoms to the oxygen atoms in one molecule of
carbon dioxide (CO2)? _______________________
Criss Cross Method
1.
Write down chemical symbols.
2.
List oxidation number in the upper right hand corner of each
symbol.
3.
Put (+) next to metal number and put (-) next to nonmetal
number.
4.
Criss cross oxidation numbers to new locations. Drop (+) and
(-).
5.
Rewrite the formula.
Examples:
1.
H+1 + S-2  ______________
2.
Li+1 + F-1  ______________
3.
Ca+2 + F-1  ______________
4.
Ba+2 + Cl-1  ______________
5.
K+1 + O-2  ______________
6.
Na+1 + N-3  ______________
7.
Li+1 + B-5  ______________
8.
Ba+2 + F-1  ______________