Unit 8: Ionic
Bonds
Chapter 8
Chemistry 1L
Cypress Creek High School
Part 2: Naming
and Writing
Formulas for Ionic
Compounds
Ionic Bonds – Writing Formulas
• Sodium and chlorine bond in a 1:1 ratio to form NaCl
• Calcium and chlorine bond in a 1:2 ratio for form CaCl2
• What determines each ratio & formula?
oxidation numbers
________________
Ionic Bonds – Writing Formulas
• CRISS-CROSS METHOD
– Oxidation numbers (excluding charge) of each ion trade
places to become the subscripts in the formula – must be
reduced to lowest whole number ratio; 1’s are not written
Al
3+
&
AlCl3
Cl
1-
2+
Ca
&
Ca2S2
CaS
S
2-
Ionic Bonds – Writing Formulas
• Try to predict the ratio and resulting formula for
each of the following ions based on their
oxidation numbers:
Ions
Oxidation Numbers
Ratio
Formula
Magnesium &
Oxygen
Mg2+ & O2-
1:1
MgO
Lithium &
Sulfur
Li+ & S2-
2:1
Li2S
Aluminum &
Oxygen
Al3+ & O2-
2:3
Al2O3
Sodium &
Phosphorus
Na+ & P3-
3:1
Na3P
Barium &
Fluorine
Ba2+ & F-
1:2
BaF2
Three Types of Ionic Compounds
• We will learn how to write nomenclature for:
– Binary Salts
• 2 elements: a metal and a nonmetal
– Ternary Salts
• 3 or more elements
• Includes a polyatomic ion
– Salts with Multiple Oxidation Numbers
• Can be binary or ternary
• Includes a transition metal
Binary Salt Naming
• Contains 2 elements: cation & anion
• Naming:
– Name the cation (no changes)
– Drop the end of anion and add “ide”
• Example: MgCl2 = magnesium chloride
Binary Salt Naming
• We’ve already predicted these formulas. Now,
try to predict the names for each binary salt:
Ions
Oxidation
Numbers
Ratio
Formula
Name
Magnesium &
Oxygen
Mg2+ & O2-
1:1
MgO
magnesium
oxide
Lithium &
Sulfur
Li+ & S2-
2:1
Li2S
Aluminum &
Oxygen
Al3+ & O2-
2:3
Al2O3
Sodium &
Phosphorus
Na+ & P3-
3:1
Na3P
Barium &
Fluorine
Ba2+ & F-
1:2
BaF2
lithium
sulfide
aluminum
oxide
sodium
phosphide
barium
fluoride
Name
Formula
acetate
C2H3O2- or CH3COO-
ammonium
NH4+
carbonate
CO32-
chlorate
ClO3-
chlorite
ClO2-
chromate
CrO42-
cyanide
CN-
dichromate
Cr2O72-
hydrogen carbonate
HCO3-
hydroxide
OH-
hypochlorite
ClO-
nitrate
NO3-
nitrite
NO2-
perchlorate
ClO4-
permanganate
MnO4-
phosphate
PO43-
sulfate
SO42-
sulfite
SO32-
Polyatomic Ions
• Some ions contain more
than one element - called
a polyatomic ion
• The group as a whole
has an overall charge
• Examples:
– Lithium and sulfate would
bond together to make
Li2SO4
– Ammonium and sulfur
would bond together to
make (NH4)2S
Ternary Salt Naming
• Contains 3 or more elements: cation & anion – most polyatomic
ions are anions, only cation is ammonium (NH4+)
• Naming:
– Name the cation (no changes)
– Name the anion (no changes)
• Example: Na2SO4 = sodium sulfate
• Exception: When ammonium is paired with an element anion
– NH4Cl = ammonium chloride
Ternary Salt Formulas
• You must use parentheses if you have more
than one polyatomic ion. Be sure to crisscross the oxidation numbers and write it
OUTSIDE of the parentheses.
+
3+
2-
Al
& SO3
Al2(SO3)3
K
3-
& PO4
K3PO4
Ternary Salt Formulas & Naming
• Try to predict the formulas and names for each
ternary salt:
Ions
Oxidation
Numbers
Ratio
Formula
Name
Potassium &
Hydroxide
K+ & OH-
1:1
KOH
potassium
hydroxide
Calcium &
Carbonate
Ca2+ & CO32-
1:1
CaCO3
calcium
carbonate
Barium &
Nitrate
Ba2+ & NO3-
2:1
Ba(NO3)2
Sodium &
Phosphate
Na+ & PO43-
1:3
Na3PO4
Ammonium &
Sulfur
NH4+ & S2-
1:2
(NH4)2S
barium
nitrate
sodium
phosphate
ammonium
sulfide
Salts with Multiple Oxidation #s Naming
• Transition elements can form more than one type of
positive ion.
– For example, copper can form both Cu+ and Cu2+
ions, and iron can form both Fe2+ and Fe3+ ions.
– Zinc and silver are two exceptions – they only have
one oxidation number
• The zinc ion is Zn2+ and the silver ion is Ag+.
• Naming:
– Name the cation
– Put the roman numeral representing the oxidation # of the
metal in parentheses (do not indicate the charge)
– Name the anion, changing the ending to “ide” (binary) or
naming the polyatomic ion (ternary)
• Example:
– FeCl2 = iron (II) chloride
– FeCl3 = iron (III) chloride
Salts with Multiple Oxidation
Numbers Practice
Ions
Oxidation
Numbers
Ratio
Formula
Name
Copper &
Nitrate
Cu+ & NO3-
1:1
CuNO3
copper (I)
nitrate
Lead &
Oxygen
Pb4+ & O2-
2:1
PbO2
Cobalt &
Hydroxide
Co3+ & OH-
3:1
Co(OH)3
cobalt (III)
hydroxide
Nickel &
Phosphate
Ni2+ & PO43-
2:3
Ni3(PO4)2
Cr2+ & S2-
1:1
nickel (II)
phosphate
chromium
(II) sulfide
Chromium &
Sulfur
CrS
lead (IV)
oxide