Objectives
•Name simple ionic compounds.
•Predict the charge of a transition metal cation in an ionic compound.
•Write chemical formulas for simple ionic compounds.
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Writing Ionic Formulas What is the chemical formula for aluminum fluoride?
1.List the elemental symbols for each ion (with the cation first)
2. Write the charges as superscripts for each ion.
3. Criss-cross values of charges
4. Write the chemical formula, indicating with subscripts how many of each ion are needed to make a neutral compound.
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• Ionic compounds are made of ions (charged particles)
– Ionic compounds are neutral; they have no net charge because the positive and negative charges offset each other
– The ions are held together in crystals by attractions between the positive and negative ions

What is the formula for the compound made of Ca 2+ cations and Cl 1anions?
Total charges of possible formulas are shown:
CaCl:
Ca
2
Cl:
CaCl
2
:
1Ca
2 Ca
1 Ca
2+
2+
2+
+ 1 Cl
+ 1 Cl
+ 2 Cl
1-
1-
1-
(2+) + (1-) = 1+
(2+) + (2+) + (1-) = 4+
(2+) + (1-) + (1-) = 0
The only formula that is neutral is CaCl
2

Use the crisscross to find the formula of an ionic compound
1.
Write the cation and anion symbols with ionic charges.
For calcium chloride,
Ca 2+ Cl 1-
2.
Make the number in the positive charge into a subscript for the anion. Make the number in the negative charge into a subscript for the cation. Ignore the – and + signs
Ca 2+ Cl 1-
Ca
1
Cl
2
= CaCl
2
3.
If necessary, reduce the resulting formula to its smallest whole-number ratio. To do this, divide all subscripts by the largest common factor

2+
1-

3+
2-

• Some metal atoms form ions with different charges under different conditions. To specify the charge for these ions, Roman numerals are used in parentheses after the name of the metal. These include: copper, lead, iron, mercury.
• Check your ion reference sheet!!

Write the formula for tin (IV) oxide
The roman numeral IV means that tin has a 4+ charge; the ions are Sn 4+ and O 2-

Give the formula for a compound containing a. Na + and Cl b. Mg 2+ and Cl c. Li + and N 3d. Al 3+ and O 2-

• Write ionic formulas for the following ionic compounds:
• Lithium oxide
• Beryllium chloride
• Titanium (III) nitride
• Magnesium oxide

Naming Ionic Compounds
• Names the cation first. (just name of metal)
• Example: when an atom of sodium loses an electron, a sodium ion, Na + , forms.
• Names the anion second. (name of non metal, change ending to –ide)
• Example: when an atom of fluorine gains an electron, a fluor ide ion, F – , forms.
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Naming Ionic Compounds
• Some cation names must show their charge.
• Iron can form two different cations. Fe
2
O
3 is made of Fe 3+ ions, so it is named iron( III )oxide. FeO is made of Fe 2+ ions, so it is named iron( II ) oxide.
• To determine the charge of a transition metal cation, look at the total charge of the compound.
• You can tell that the iron ion in Fe
2
O
3 has a charge of 3+ because the total charge of the compound must be zero, and an oxide ion, O 2– , has a a charge of 2–.
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Copyright © by Holt, Rinehart and Winston. All rights reserved.

Naming Ionic Compounds
Chapter menu Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.