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Ionic Compounds
This is Important!
• On the Periodic Table… remember where to:
and the nonmetals find the metals
If You Don’t Remember How to Tell Metals From
Nonmetals, Nothing in This Chapter Will Make Sense!
Ionic Compounds
There are two types of
ionic compounds…
1. Binary ionic compounds and…
2. Ionic compounds that contain
“polyatomic ions”.
Binary Ionic Compounds
Type 1: Binary Ionic Compounds
1. “Binary” means 2…
(as in “bicycle”… “2 wheels”)
A binary ionic compound has only…
…2 elements:
(example: BaCl2)
1.The first element is always a metal!
2.The second element is always a nonmetal!
Type 1: Binary Ionic Compounds
• “2 elements” means just that… “2 elements”!
There can be more than one ion of an element!
• Example: AlF3
AlF3 contains only 2 elements: Al & F.
AlF3 has 1 Al+3 ion, and 3 F-1 ions.
{metal (+) & nonmetal (-)}
The subscript tells you how many ions are in
the compound… (a “1” is understood and not written)
Naming Binary Ionic Compounds
Naming Binary Ionic Compounds
• To name a binary ionic compound…
1. Write the name of the metal ion (+)…
(this is just the name of the metal)
2. Write the name of the nonmetal ion (-)…
(the nonmetal ion has the same “root” as
the nonmetal, but with an “-ide” suffix).
Examples: “chlorine” becomes “chloride”
“oxygen” becomes “oxide”
“nitrogen” becomes… “nitride”
That’s It!!
Naming Binary Ionic Compounds
Just write the metal ion name first, then the
nonmetal ion name second!
(remember the “ide” nonmetal ending)
Practice: (name these)…
K2S
MgO
Sr3As2
potassium sulfide
magnesium oxide
strontium arsenide
Writing the Formula of a Binary Ionic Compound
• Remember, metals are always (+) because
they lose electrons, and
• Nonmetals are always (-) because
they gain electrons!!
• In any ionic compound,
the total (+) must EQUAL the total (-)!!
Writing Binary Ionic Compounds
• To write a binary ionic compound formula…
• …you must know the charge …
• …of the metal ion and the nonmetal ion!
• There are two ways to know these…
…Memorize them, or
…Look at the periodic table!
Guess which is easier?!
Writing Binary Ionic Compounds
You Guessed it!
The “representative” elements are easy! +1
+2
+3
Each family has
its own charge! -3 -2 -1
0
Noble gas
“wannabe’s”,
remember?
In Family IVA (14), only Sn and Pb form ions
Writing Binary Ionic Compounds
IVA
• The transition metals do not follow any simple
rules. (Many can even have two possible
charges!)
• Some must be memorized, but, there IS an
easy system for the others…
• The Roman Numeral after the name gives you
the (+) charge!
• Examples: “copper(I)” = Cu+1
“iron(III)” = Fe+3
“lead(IV)” =
Writing Binary Ionic Compounds
Pb+4
• IONIC COMPOUNDS ARE NEUTRAL!!
• Be sure the (+) charges = the (-) charges!
• Example: “aluminum fluoride”
Writing Binary Ionic Compounds
aluminum ions are Al+3 fluoride ions are F-1
Al+3 F-1 AlF3 (Al+3 + F-1 + F-1 + F-1)
Adds up to zero! The compound has
NO charge!
Practice: write the formula for:
Writing Binary Ionic Compounds
calcium fluoride
lithium phosphide
aluminum oxide
+2
-1 CaF2 +3
Al2O3
+1
-3
Li3P
-2
copper(II) chloride CuCl2 Cu+2 and Cl-1
Writing Binary Ionic Compounds
Ionic formulas are “formula units” of ionic
compounds…
…ionic compounds can’t form molecules!
Remember to reduce any ionic formula to a
lowest ratio… Example: barium oxide
Ba+2 O-2 Ba2O2? Reduce to “BaO”
Special Note: be SURE to write element symbols
clearly! Lower and upper case letters must be obvious!
Compounds Containing Polyatomic Ions
Type 2: Ionic Compounds
Containing “Polyatomic Ions”
•Polyatomic ions are GROUPS of atoms
with a charge!
(most will have a negative (-) charge, just
like a non-metal ion)
You will be given a list of these to use…
O
• “poly” means “many”, so…
• “polyatomic” means “many atoms”!
• (These are ions made of groups of atoms)!
Polyatomic Ions
An example: the
polyatomic ion,
“nitrate”… N
O O
-1
This group of atoms carries a charge of (-1).
Nitrate’s
formula is:
NO3-1
…contains 1 nitrogen and 3 oxygen atoms!
Naming Compounds with Polyatomic ions
Naming Ionic Compounds With
Polyatomic Ions
• To name an ionic compound with polyatomic
ions is really EASY…
1.Write the name of the positive ion (+)…
(usually the name of the metal)
2.Write the name of the negative ion (-)…
(usually the polyatomic ion)
That’s IT!!
• Example: Mg(NO3)2 “magnesium nitrate”
Writing the Formula of a Compound That Contains
Polyatomic Ions
• To write a formula using polyatomic ions,
…you must know the formula and charge …
…of the metal ion and the polyatomic ion.
• The metal ions you know (periodic table)…
…you will have a list of polyatomic ions
with their formulas and charges.
Formulae with Polyatomic ions
• In ALL ionic compounds, the total (+) must be
equal to the total (-)!!
• Just look at the charges, and make sure they
add up to zero.
Formulae with Polyatomic ions
“sodium” = Na+1 “carbonate” = CO3-2
Na+1 CO3-2
“Na2CO3”
+ Na+1 Na+1 + CO3-2
Adds up to zero!
Example: “sodium carbonate”
• What if more than one polyatomic ion is needed?
• Wrap the polyatomic ion in parenthesis!
• Example: “aluminum sulfate”
aluminum ions are Al+3 sulfate ions are SO4-2
Al+3 SO4-2
(Al+3 + Al+3 +
Adds up to zero!
Formulae with Polyatomic ions
SO4-2 + SO4
-2 + SO4-2)
2 Al+3 3 SO4-2
Al2(SO4)3
A Final Note
•Some ionic compounds “collect” water from
the moisture in the air.
•They trap this “collected water” in their
crystals.
•When they have trapped this water, they are
called “hydrates”.
•Their formula includes water, written after a
raised dot: MgSO4 · 5H20
(magnesium sulfate pentahydrate)
*(Prefixes
in your
notes) *
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