WRITING FORMULAS

 

1.)  Does the name end with “-ide”?

          à  If yes, go to # 2

à     If not, go to # 4

 

2.)  Is the second word “hydroxide”?

          à  If yes, go to # 4

à     If no, go to # 3

 

3.)  Is the first word “ammonium”?

          à  If yes, go to # 4

à     If no, go to # 5

 

4.)  The compound is tertiary (or ternary – compound has more than 2 elements).

      Is the first word the name of a metal or “ammonium”?

          à  If first word is name of a metal, go to # 7

          à  If first word is “ammonium”, go to # 8

 

5.)  The compound is binary (has only two elements). 
      Is the first word the name of a nonmetal or a metal?

          à  If first word is name of a nonmetal, go to # 6

à     If first word is name of a metal, go to # 7

 

6.)  To write formula for compound:

          ~ Write the symbol for the first element.
          ~ Prefix of first word tells subscript of first element.

          ~ Write symbol for second element.

          ~ Prefix of second word tell subscript of second element.

 

7.)  To write formula for compound:

          ~ Write the symbol for the element with its oxidation number.

          ~ Write the symbol for the second element with its oxidation number (if binary cmpd)  OR

            Write the formula for the polyatomic ion with its oxidation number (if tertiary cmpd) 

          ~ Cross out the “+” and “-“.

          ~ Reduce (simplify) the numbers if possible.
          ~ “Criss-cross” the numbers.  (The oxidation number of the first part becomes the subscript
            of the second part.  The oxidation number of the second part becomes the subscript of
            the first part.)

 

8.)  To write formula for compound:

          ~ Write “NH4+1

          ~ Write the symbol for the second element with its oxidation number  OR

            Write the formula for the polyatomic ion with its oxidation number 

          ~ Cross out the “+” and “-“.

          ~ Reduce (simplify) the numbers if possible.
          ~ “Criss-cross” the numbers.  (The oxidation number of ammonium becomes the subscript
            of the second part.  The oxidation number of the second part becomes the subscript of
            ammonium.)

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EXAMPLES:
1.) calcium oxide

2.) carbon tetrachloride

3.) ammonium chromate

4.) lead (II) nitrate

5.) aluminum hydroxide

6.) iron (III) bromide

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