Ionic Compounds
The Loss or Gain of Electrons
Stable Atoms
We know that atoms that are stable have either:
 A filled outer energy level – eight electrons (the
octet rule).
 Elements will lose or gain electrons to achieve
this state.
 Use the periodic table to see how many
electrons the atom needs to be stable.
Ex. O has 6, but wants 8. It adds 2e’s;
It makes the ion O-2
Ions
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Ionic compounds start with ions
When naming an anion we will take the
beginning of the name and add –ide.
Ex. Cl- is called chloride, not chlorine
When naming a cation we just use the name of
the element plus the word ion.
Ex. Na+ is called sodium ion
Ionic Compounds
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Ionic compounds are called salts.
Consist of a metal and a nonmetal.
A cation and an anion. There can be multiples of
each.
It is the electrostatic attraction (opposites
attract) between the positive cation and the
negative anion that holds the compound in the
solid state.
Characteristics of Ionic Compounds
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Strong bonds.
Solids.
High melting points.
Exist as crystals with repeating units
Can be soluble (dissolve in water) or insoluable
Naming Ionic Compounds
Always name the cation first.
 Change the suffix of the anion to –ide.
 If the cation is a transition element the name
MUST contain a Roman numeral. This
represents its charge or oxidation state.
Example:
KI – potassium iodide
SrCl2 – strontium chloride
FeF3 – iron(III) fluoride.
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Polyatomic Ions
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Polyatomic ions are ions that consist of more
than one element.
It is very important to keep in mind that the
charge on the polyatomic ion belongs to the
entire molecule, not to just one atom within the
molecule.
NO3- nitrate polyatomic ion.
SO4-2 sulfate polyatomic ion.
Polyatomic Ions
You are responsible for memorizing the following polyatomic
ions with respect to their formulas, names, and charges:
(They are found on your ion chart)
CH3COO-1 (C2H3O2-1)
NH4+1
CO3-2
CrO4-2
OH-1
NO3-1
NO2-1
PO4-3
SO4-2
SO3-2
acetate
ammonium
carbonate
chromate
hydroxide
nitrate
nitrite
phosphate
sulfate
sulfite
Polyatomic Ions
Ionic compounds containing polyatomic ions are
named by:
 Naming the cation.
 Naming the polyatomic ion.
NaNO3 – sodium nitrate
Mg(OH)2 – magnesium hydroxide
Writing Formulas
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Two methods to writing formula
First method- add up charges;
Write the cation first.
Write the anion last.
First method- The sum of the oxidation
numbers or charges must equal zero. Ex.
Calcium chloride
Ca+2 2xCl- = -2
CaCl2
Second method – criss-cross
Ca+2 Cl-1 = CaCl2
Writing and Naming Ionic Formulas
Name the following ionic compounds:
SrO
Al(CH3COO)3
CuSO4
strontium oxide aluminum acetate copper(II) sulfate
KNO3
potassium nitrate
CrPO4
chromium(III) phosphate
BaI2
barium iodide