Polyatomic Ions
Compounds
&
Nomenclature
Objectives Covered Today
6. Define a polyatomic ion
7. C4.2c Name compounds containing a
polyatomic ion.
8. C4.2d Given the name of a compound
containing a polyatomic ion, write its formula.
Objective 6
Define a polyatomic ion
Polyatomic Ion: An ion (either positively or
negatively charged) composed of two or more
atoms.
Is it possible to predict charges?
• Based on covalent bonding (next chapter)
• Charges of polyatomic ions are still based on
the overall stability of the molecule
• Not as predictable as monatomic ions
• These will have to be memorized
• However, this becomes easy with practice
Common Examples
HCO32-
Bicarbonate Ion
PO43-
Phosphate Ion
NH4+
Ammonium Ion
NO3-
Nitrate Ion
Objective 7
Name compounds containing a polyatomic ion
Example: NaNO3
1. If the compound contains a metal cation, the
name of the metal comes first.
Objective 7
Name compounds containing a polyatomic ion
Example: NaNO3
1. If the compound contains a metal cation, the
name of the metal comes first.
Sodium
Objective 7
Name compounds containing a polyatomic ion
Example: NaNO3
2. The second part of the name is just the name
of the polyatomic ion
Sodium
Objective 7
Name compounds containing a polyatomic ion
Example: NaNO3
2. The second part of the name is just the name
of the polyatomic ion
Sodium Nitrate
What if the Polyatomic Ion comes
first?
NH4+ (Ammonium ion) is a positive ion while still
being polyatomic
If you are using a polyatomic cation you just use
the ion’s name, and it will be written first
NH4Cl
What if more than one Polyatomic Ion
is needed?
Compounds must be neutral!
• If > 1 polyatomic ion is needed in a formula, it
will be put in parentheses before the subscript
• When writing its name, it will just remain the
name of the polyatomic ion
Al2 (SO4)3
Objective 8
Given the name of a compound containing a
polyatomic ion, write its formula.
Example: Potassium Carbonate
1. Determine atomic symbols and charges
Objective 8
Given the name of a compound containing a
polyatomic ion, write its formula.
Example: Potassium Carbonate
1. Determine atomic symbols and charges
K+
CO32-
Objective 8
Given the name of a compound containing a
polyatomic ion, write its formula.
Example: Potassium Carbonate
2. Determine number of each ion to balance charges
K+
CO32-
Objective 8
Given the name of a compound containing a
polyatomic ion, write its formula.
Example: Potassium Carbonate
2. Determine number of each ion to balance charges
2K+
1CO32-
Objective 8
Given the name of a compound containing a
polyatomic ion, write its formula.
Example: Potassium Carbonate
3. Using symbols for both ions and proper subscripts,
write the formula
K2CO3
Practice Examples
1.
BeSO3
2.
NaC2H3O2
3.
Ca(NO3)2
4.
Aluminum
Nitrite
5.
Iron (II)
Hydroxide
6.
Ammonium
Phosphate
Happy Thanksgiving Break!