Chemical Formulas and Names for
Ionic Compounds
Terminology Review:


A chemical formula uses chemical
symbols to represent a particular compound.
Compound – 2 or more different elements
chemically bonded together in a fixed
proportion
What are Ionic Compounds?
Ionic compounds
- when one or more electrons are transferred from
one atom to another, creating a neutral
compound
- pure substances usually consisting of one metal
(donor or giver of electrons – therefore pos. charge) and one
non-metal (receiver of electrons – therefore neg. charge)

Some Properties of Ionic Compounds:
Crystal Lattice Solid
-
-
high melting points
ability to form crystals
dissolve in water to form solutions that
conduct electricity
solid at room temperature
Conductivity
Soluble in Water
How are Ionic Compounds formed?
Ionic bonds - attraction
between oppositely
charged ions
How do ions form?
- when one or more
electrons move from
a metal atom over to
a non-metal atom
Rules to follow when writing Formulas
and Naming Ionic Compounds:
a) & b)
Ion formed from elements
a) Write the symbol for the metal first, then the non-metal.
b) Determine the ion charge each element would form.
Write the charge to the upper right of the symbol.
Elements to
Combine
a) b)
Ion formed
(Element symbol
and charge)
Mg2+
Magnesium
Chlorine
Cl-
REVIEW – What’s the Charge?
Remember:
Look at the valence electrons and ask yourself “What’s
easiest?”.
Let’s review……….
Note the names of the non-metals when they turn into ions.
Predicting Ionic Charges
Group 1: Lose 1 electron to form 1+ ions
H+
Li+ Na+
K+
Predicting Ionic Charges
Group 2: Loses 2 electrons to form 2+ ions
Be2+
Mg2+
Ca2+
Sr2+
Ba2+
Predicting Ionic Charges
B3+
Al3+
Ga3+
Group 13: Loses 3
electrons to form
3+ ions
Predicting Ionic Charges
Neither! Group 14
elements rarely form
ions.
Group 14: Lose 4
electrons or gain
4 electrons?
Predicting Ionic Charges
N3- Nitride
P3- Phosphide
As3- Arsenide
Group 15: Gains 3
electrons to form
3- ions
Predicting Ionic Charges
O2- Oxide
S2- Sulfide
Se2- Selenide
Group 16: Gains 2
electrons to form
2- ions
Predicting Ionic Charges
F1-Fluoride
Br1- Bromide
Cl1-Chloride
I1- Iodide
Group 17: Gains 1
electron to form
1- ions
Predicting Ionic Charges
Group 18: Stable
Noble gases do not
form ions!
Predicting Ionic Charges
Groups 3 - 12: Many transition elements
have more than one possible oxidation state.
Iron(II) = Fe2+
Iron(III) = Fe3+
Predicting Ionic Charges
Groups 3 - 12: Some transition elements
have only one possible oxidation state.
Zinc = Zn2+
Silver = Ag+
c) Determine the number of each
ion needed to balance the charge.
Elements to
Combine
a) b)
Ion formed
(Element symbol
and charge)
c)
Balance the
charges
Cl-
Magnesium
Chlorine
Mg2+
Criss-Cross Rule: Place the
charge of one ion as the
subscript of the other ion.
Cl-
Mg2+
Cl-
Total: 2 + and 2 –
Overall charge = 0
d) Write the chemical formula
Rewrite the symbols together (no spaces) with the
number of each needed as subscripts, reduce if possible
Elements to
Combine
a) b)
Ion formed
(Element symbol
and charge)
Magnesium
Chlorine
Mg2+ Cl-
c)
Balance the
charges
Mg2+
d)
Write the
chemical
formula
ClCl-
MgCl2
e) Write the name of the metal first,
then the nonmetal by changing the
ending to “ide”.
Elements to
Combine
a) b)
Ion formed
(Element symbol
and charge)
Magnesium
Chlorine
c)
Balance the
charges
d)
Write the
chemical
formula
e)
Name the compound
MgCl2
Magnesium Chloride
ClMg2+ Cl-
Mg2+
Cl-
Polyatomic Ions
A polyatomic ion
• is a group of atoms.
• has an overall ionic charge.
Some examples of polyatomic ions are
NH4+
ammonium
NO3− nitrate
OH−
NO2−
hydroxide
nitrite
CO32− carbonate
PO43− phosphate
HCO3− hydrogen carbonate
(bicarbonate)
Naming Polyatomic Ions
The names of common polyatomic anions
• end in ate.
NO3− nitrate
PO43−
phosphate
• with one oxygen less end in ite.
NO2− nitrite
PO33−
phosphite
Naming Compounds with
Polyatomic Ions.
• The positive ion is named first, followed by
the name of the polyatomic ion.
NaNO3
sodium nitrate
K2SO4
potassium sulfate
(NH4)3PO3
ammonium phosphite
Writing Formulas with Polyatomic
Ions.
• The Criss-Cross Rule still applies
Na+ and NO3− -> NaNO3
• with two or more polyatomic ions has the
polyatomic ions in parentheses.
Mg2+ and 2NO3− -> Mg(NO3)2
subscript 2 for charge balance