Transcript part 2.writing chemical formulas for ionic compounds

Part 2: Writing and Naming
Chemical Formulas for Ionic
Compounds with Polyatomic ions
(go over worksheet from last day
first)
Writing Chemical Formulas for
Compounds Containing Polyatomic Ions
1. Write the atom’s symbols with their
combining capacities (as superscripts).

Note that the polyatomic ion is treated
as a single entity. Also, most polyatomic
ions end in “ate” or “ite”

Although there are several atoms in
that ion, it is treated as a single “atom”
with a combining capacity.
2. Crisscross the combining capacities,
and write them (WITHOUT the +
or -) as subscripts.

Please note that if the polyatomic
species ends up with a subscript
greater than 1, brackets must be
put around the polyatomic species.
3. Write the final chemical formula.
 If there are any 1’s, remove them.
 If subscripts are multiples of each
other, reduce them
 NEVER reduce any subscripts that
belong to the original polyatomic ion.
Examples:
1.lithium nitrate
•
LiNO3
2.calcium carbonate
CaCO3
3. copper (II) sulphate
CuSO4
4.magnesium hydroxide
Mg(OH)2
5.ammonium chloride
•
NH4Cl
6.ammonium phosphate
(NH4)3PO4
Writing Names for Compounds
Containing Polyatomic Ions
1.
Write the name of the metal or the polyatomic ion
with a positive valence number first. (At this level,
Ammonium (NH3) will be the only positively charged
polyatomic used)
2.
Followed by the name of the non-metal, or the
polyatomic ion with a negative valence number).

If the second element is a non-metal, remove
the ending and add “ide”.

If the second part of the formulas is a
polyatomic ion, DO NOT change the ending.
Examples:
1. (NH4)2S
Ammonium Sulphide
2. Na2CO3
Sodium Carbonate
3. ZnSO4
Zinc Sulphate
4. Bi3(PO3)5
(Careful, trick question!)
Bismuth (V) Phosphate
Friendly Note:
• Compounds may contain both transition
metals and polyatomic species,
therefore you may need to combine
more than one set of rules.