Learning Objectives:
What is a polyatomic ion?
How do polyatomic ions combine with
other ions?
How are compound names determined?
6.1 POLYATOMIC IONS – STUDENT NOTES,
monatomic
Polyatomic
ions
Negative
positive
The prior ions in the notes were all charged single atoms. These are called monatomic ions.
The other important class of ions includes groups of atoms that act together to create ions and ionic bonds.
Since these are ions made of many atoms they are called Polyatomic ions
The majority of polyatomic ions have a Negative charge but there is one with a positive charge.
REPRESENTING POLYATOMIC IONS
Polyatomic ions are represented with square brackets to illustrate that they are a group that acts as a unit or
an element. The charge is shown at the upper right corner of the brackets.
If the ion is not combined with something its charge is shown to the upper right of its formula.
(Fill in the remaining boxes in the following table)
Name
Ammonia Ion
Nitrate Ion
Sulfate Ion
1-
2-
Lewis Structure
Formula
NH4
Charge
1+
1+
NO3
SO4
1-
2-
WHEN POLYATOMIC IONS COMBINE
When polyatomic ions combine with other ions to create stability they follow the same rules as all ions. They combine to
create a neutral compound. If more than one of a polyatomic ion is included in a combination it is placed in parenthesis.
A subscript outside the parenthesis indicates the number of the polyatomic ion included in the structure.
Answer the questions below related to the Formula for Calcium Nitrate:
How many Calcium atoms are present? 1
Now many Oxygen atoms are present? 6
How many Nitrogen atoms are present?
How many Nitrate Ions are present? 2
2
NAMING COMPOUNDS
The names of chemical compounds are created according to rules set by the International Union off Pure and
Applied Chemistry (IUPAC). There are separate rules for IONIC AND MOLECULAR COMPOUNDS.
IONIC COMPOUNDS




Names have two parts.
First part names the cation (+ ion)
o Rules are different if H+ is the cation
Second part names the anion ( - ion)
Anion has the suffix –IDE
EXAMPLES:
NaCl is named Sodium Chloride
CaBr2 is named Calcium Bromide
WHEN THE CATION IS A METAL WITH MORE
THAN ONE CHARGE
Several transitions metals like Copper (Cu) can
form multiple cations
EXAMPLE: Copper forms Cu2+ and Cu1+

Rules are the same as before except the
cation (+ ion) includes roman numerals to
indicate its charge.
MgF2 is named Magnesium Fluoride
EXAMPLES:
CuCl is named Copper (I) Chloride
CaNO3 is named Calcium Nitrate
CuS is named Copper (II) Sufide
MOLECULAR COMPOUNDS
The name and formula of a molecular compound describe the type and number of
atoms in a molecule of a compound.
These rules are general rules which means they are not strictly followed so there will be
cases where the rules don’t apply. For the purpose of this course the rules will always
apply.
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

Prefixes for Naming
Compounds
# of
Atoms
Prefix
1
2
3
4
5
6
7
8
9
10
MonodiTriTetraPentaHexaHeptaOctaNonaDeca-
Most metallic element appears first
o If the two elements are in the same group the one closest to the bottom
appears first
The second element is changed to end in the suffix – IDE.
Prefixes are attached to the element names to indicate the number of that
element in the compound.
o See the table of prefixes
o The prefix mono- , for the number one, is not always included.
Which compound is dinitrogen tetroxide? A or B
Which compound is nitrogen dioxide? A or B
EXAMPLE OF A COMPOUND THAT DOES NOT FOLLOW THE RULES: What would water be called if it followed
the rules? Hydrogen Hydroxide Why is it not called this? It was already known as water and the name
stuck.