CH 9: Chemical Names & Formulas
Section 9.1 – Naming Ions
• OBJECTIVES:
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– Identify the charges on monatomic ions by
using the periodic table, & name the ions.
– Define a polyatomic ion & write the names &
formulas of the most common polyatomic ions.
– Identify the two common endings for the
names of most polyatomic ions.
Group 1: 1+
Group 2: 2+
Group 13: 3+
Group 14: 4+/4Group 15: 3Group 16: 2Group 17: 1Group 18: 0
Predicting Ionic
Charges
1+
0
4+/43- 2- 13+
2+
An Anion is…
A Cation is…

A positive ion.
Formed by losing electrons.
More protons than electrons.
Metals can lose electrons
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A negative ion.
Has gained e-.
Nonmetals can gain e-.
Charge is written as a
superscript on the right.
K1+
Has lost 1e- (no
name change for
positive ions)
F-
Ca2+
Has lost 2e-
O2-
Has gained 1e- (-ide is
new ending = fluoride)
Gained 2e- (oxide)
Naming cations
• Two methods are used when more than one
charge is possible:
1) Stock system – modern system that uses Roman
numerals in ( ) to indicate the numerical value
2) Classical method – older system that uses root word
with suffixes (-ous, -ic); less common method
• Cation – always keeps its name as is
• Most transition metals have more than one
oxidation state
– Indicate oxidation state as a Roman numeral in ( )
after the name of the metal (Table 9.2, p.255)
Naming
Anions
• Anions do not
typically have
multiple
oxidation states;
they have a single
charge
• Change the
monatomic
element ending
to -ide
• F- a Fluorine
atom will become
a Fluoride ion.
Practice by…naming the left column and
writing symbols for the right column:
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Na1+
Ca2+
Al3+
Fe3+
Fe2+
Pb2+
ClN3BrO2F-
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Potassium ion
Copper (II) ion
Chromium (VI) ion
Barium ion
Mercury (II) ion
Lead (IV) ion
Sulfide ion
Iodide ion
Phosphide ion
Selenide ion
Arsenide ion
Polyatomic ions are…
• Groups of atoms that stay together and have an
overall charge, and one name.
• Usually end in -ite (fewer oxygens) or -ate (more
oxygens); some end in -ide
• Nitrite: NO2- and Nitrate: NO3• Sulfite: SO32- and Sulfate: SO42• Hydroxide: OH- and Cyanide: CNIf the polyatomic ion begins with H, then combine the word
hydrogen with the polyatomic ion present:
H1+ + CO32- →
HCO31hydrogen + carbonate → hydrogen carbonate ion
1
Sections 9.2 – 9.3 Naming and Writing Formulas
for Ionic & Molecular Compounds
Writing Ionic Compound Formulas
Examples: Barium nitrate and Ammonium sulfate
• OBJECTIVES:
Writing Ionic Compound Formulas
3. Balance charges , if necessary,
using subscripts. Use
parentheses if you need more
than one of a polyatomic ion.
Use the criss-cross method to
balance subscripts.
( NH4+ ) SO42-
3. Balance charges , if necessary,
using subscripts. Use parentheses if
you need more than one of a
polyatomic ion. Use the criss-cross
method to balance the subscripts.
2
= (NH4)2SO4
9.2 – 9.3 Naming/Writing Formulas for Ionic/Molecular Compounds
Writing Ionic Compound Formulas
Example: Magnesium carbonate, Zinc hydroxide, and
Aluminum phosphate
Fe3+ Cl-3
2. Check to see if charges are
balanced.
2
= Ba(NO3)2
2. Check to see if charges are
balanced.
Example: Iron (III) chloride and Aluminum sulfide
1. Write the formulas for the
cation and anion, including
CHARGES!
Ba2+ ( NO3- )
1. Write the formulas for the
cation and anion, including
CHARGES!
– Apply the rules for naming and writing formulas for
binary ionic compounds.
– Apply the rules for naming and writing formulas for
compounds containing polyatomic ions.
– Interpret the prefixes in the names of molecular
compounds in terms of their chemical formulas.
– Apply the rules for naming and writing formulas for
binary molecular compounds.
Mg2+ CO32-
1. Write the formulas for the
cation and anion, including
CHARGES!
= FeCl3
They are balanced!
2. Check to see if charges are
balanced.
3. Balance charges , if necessary,
using subscripts. Use parentheses
if you need more than one of a
polyatomic ion. Use the criss-cross
method to balance the subscripts.
S2Al3+
2
3
= Al2S3
= MgCO3
Zn2+( OH-)
= Zn(OH)2
2
Al3+ PO43-
They ARE balanced; = AlPO4
Naming Ionic Compounds
1. Name the cation 1st, keeping its name as is, then the anion
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Monatomic cation = name of the element; Ca2+ = calcium ion
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Monatomic anion = root + -ide; Cl- = chloride
2. Binary ionic compound (2 elements) = cation + anion
CaCl2 = calcium chloride
3. Some metals have more than one oxidation state (usually the
transition metals and some representative metals)
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Use a Roman numeral in their name: PbCl2 – use the anion to find the
oxidation state of the cation; since chloride is always 1Pb2+ is the lead (II) cation; PbCl2 = lead (II) chloride
4. Ionic compounds with more than 2 elements contain polyatomic
ions; polyatomic ions keep their name as is
NaOH = sodium hydroxide
NH4Cl = ammonium chloride
Fe2(SO4)3 = iron (III) sulfate
Things to look for:
If cations have ( ), the number in ( ) is their charge.
If anions end in -ide they are off the periodic table if monoatomic,
but some polyatomics end in -ide
If anion ends in -ate or -ite, then it is polyatomic
1)
2)
3)
Practice by writing the formula or name as required…
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Iron (II) Phosphate
Stannous Fluoride
Potassium Sulfide
Ammonium Chromate
MgSO4
FeCl3
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