Writing Chemical Formulas
When writing chemical formulas for binary ionic compounds(compounds made
with just a positive and negative ion; bi= 2), oxidation numbers are used. Here is the
process:
1. Write the symbol for the element with the positive oxidation number (the
metal) followed by the oxidation number. The oxidation number is written as
a superscript.
2. Write the symbol for the element with the negative oxidation number (the
nonmetal) followed by the oxidation number after the metal. The oxidation
number is written as a superscript.
3. Cross the oxidation number over to the other element and write it as a
subscript (sub = below; script = to write).
Special cases
1. If the oxidation numbers are the same, no subscripts are written.
2. If an oxidation number is going to be written after a polyatomic ion, place the
entire ion inside parenthesis with the subscript following it.
3. Some metals have more than one oxidation number. These are usually written
with a roman numeral after them. The roman numeral is the oxidation
number.
When finished writing the formula, the sum of all the oxidation numbers in the
formula will equal zero. If it does not, the formula is not correctly written.
What is a binary compound?
Explain how oxidation numbers are used in writing formulas.
When are subscripts not written in a formula?
When are parenthesis used in writing formulas?
In a correctly written formula, what must the sum of the oxidation numbers equal?
How would you determine which oxidation number to use for copper?
Write formulas for each of the following:
Potassium Nitride
Barium Sulfite
Copper(II) Carbonate
Copper(II) Chlorate
Aluminum Chloride
Ammonium Phosphate
Sodium Sulfide
Sodium Bicarbonate
Iron(III) Bisulfate
Lead Chloride