Names and Formulas
for Ionic Compounds
Types of ions
• Monatomic ion
– ion with one atom
• Mg2+ magnesium ion
• Cl- chloride ion
• Polyatomic ion
– ion with more than one atom
• NH4+
• NO3-
ammonium
nitrate
Ionic Compound Marriage
Metals are like men
Nonmetals are like woman
Typically who changes their last name?
Naming Ca”t”ions
• Monatomic cation name stays the same
– Sodium, Na goes to sodium ion, Na+
– Calcium, Ca goes to calcium ion, Ca 2+
• Polyatomic cation - look up in chart
–NH4+ ammonium
Naming Anions
• The name changes in a monatomic anion
• The ending for a monatomic anion is ______ide
(like a bride changes her last name)
– chlorine, Cl goes to chloride ion, Cl– Fluorine, F goes to fluoride ion, F-
• Polyatomic anion look up in chart
– OH- hydroxide
– SO42- sulfate
Question Time
Given the neutral atom, give the charge and
name of the monatomic ion that will form.
(Look at periodic table group numbers for help.)
1.
2.
3.
4.
5.
Na
Cl
Mg
S
P
Na+
ClMg2+
S2P3-
sodium cation
chloride anion
magnesium cation
sulfide anion
phosphide anion
Name the following polyatomic ions.
(use your chart!)
6.NH4+
ammonium cation
hydroxide anion
7.OH−
8.SO32−
sulfite anion
9.SO42− sulfate anion
cyanide anion
10.CN−
Naming ionic compounds
• Name the cation first and then the anion
second (+ then -)
• Example: CsF
– Monatomic cations use the element name
• Cs+ = cesium
– Monatomic anions – change the ending to ide
• F - = fluoride
cesium fluoride
Will these form an Ionic Compound?
If so what will the compound name be?
1.
2.
3.
4.
5.
Mg
Al
Mg
Na
C
Al
S
O
N
S
No
Yes
two metals
aluminum sulfide
Yes
magnesium oxide
Yes
No
sodium nitride
two non-metals
Formula Unit
• Formula Unit—the smallest whole number
ratio of ions in a compound
• NaCl versus Na2Cl2
• Correct: Sodium Chloride NaCl
What will the formula be?
 In ionic compounds, we must balance charges to
form a neutral compound
 To do that, we “crisscross the charges”
 Always reduce to get the formula unit
Ca + N
Ca2+ + N3Ca3 N2
Both have a total charge of 6
(3 Ca2+ = +6; 2 N3- = -6)
Practice
1.
2.
3.
4.
5.
Given the following elements, predict the
formula. (hint first identify the ion charge)
K, Br
Ca, Cl
Li, S
Mg, N
Ba, P
Formula Unit with Polyatomic ions
• Sometimes you will need to use more than
one polyatomic ion to balance a charge.
• If so, you need to put it in parenthesis (like a
package) and use a subscript for the multiple
number
Ex: Mg2+ and NO3These charges do not balance so we must crisscross them
Mg1(NO3)2 (we don’t need the 1)
Mg (NO3)2
Transition Metal Ions
• Metals form cations
• Some transition metals only have one ionic
charge
– Silver (Ag+), Cadmium (Cd2+), Zinc (Zn2+)
• Some transition metals can take on more than
one charge.
– Copper (Cu+, Cu2+)
• Charge is determined from the number of
electrons lost
Naming Transition Metal Ions
• If a transition metal has more than one charge,
the charge is written as a Roman numeral in
parenthesis
• Some metals need a middle name
• Fe (iron) has more than one charge: 2+ and 3+
– Fe2+
– Fe3+
iron(II)
iron(III)
• If the transition metal only has one charge, no
Roman numeral is needed
Naming Ionic Compounds with
Transition Metals
Given: Fe2O3
• First find the charges of the ions
• Then name the cation followed by the anion
– Iron(III) oxide
• Try this one: Fe3P2
• the charge on iron is a 2+
• iron(II) phosphide
Question Time
Identify the charge on the transition metal:
1. copper (II) nitrate
2. gold (I) chromate
2+
1+
Name the compound:
1. FeO
2. Zn(OH)2
3. CoPO4
iron (II) oxide
zinc hydroxide
cobalt (III) phosphate