Names and Formulas for Ionic Compounds
• Cornell Notes
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5 questions
5-sentence summary
Naming Ionic Compounds
• Metal + Nonmetal
• metal always goes 1st
• Examples,
• Sodium and Chlorine  NaCl
• Calcium and Bromine  CaBr2
• Metal (the cation): no name change
• Sodium  sodium
• Nonmetal (the anion): -ide name change
• Fluorine  fluoride
• Oxygen  oxide
• Phosphorus  phosphide
Ionic Compound Formula Units
• Superscript: number to the upper right of each element
• Denotes the charge of an element
• Subscript: number to the lower right of each element
• Denotes the # of atoms of that element in the compound
• if there is no subscript, assume there is only 1
• Ex: CaBr2 (1 Ca and 2 Br in the compound)
Writing Ionic Formula Units: Cross-Over
Method
1. Find the charge of each element
2. Cation is 1st, anion is 2nd
3. “Cross over” the numbers, and write as subscripts next to
the opposite ion
4. Drop the “+” or “-” sign
5. All “1” should be dropped
6. If numbers are divisible, write the simplest ratio
Cross-Over Method Examples
1. Li and Br
 Li1+
Br1-
 Li1
2. Mg and I
 Li1 Br1
 Mg2+
 LiBr
I1 Mg1
I2
3. Al and O
 Mg1I2
 Al3+
 MgI2
O2 Al2
O3
4. Ca and S
 Al2O3
 Ca2+
S2-
S2
 Ca2S2
 CaS
 Ca2
Br1
Names and Formulas for
Ionic Compounds -
Formula Unit
• A formula unit is the simplest ratio of an ionic compound
1 Na and 1 Cl
1Ca and 2 F
Formula Unit
• For example:
• 1 Ca2+ and 1 O2- form [Ca2+][O2-]  CaO
• CaO is the formula unit for the ionic compound of Ca and O
[Ca2+][O2-]
CaO
(together,
now neutral)
Important terms
• Monatomic ion – a single-atom ion
• Example: K+, F-, Mg2+, Se2-
• Oxidation number – the charge of any ion
• Ex: oxidation number of K is +1, or Se is -2.
• Polyatomic ions – Ions made up of more than 1 atom
(charge applies to entire group of atoms)
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•
•
•
Example: SO42-  called the sulfate ion
Parenthesis can be used to group atoms in a polyatomic ion
Charge is written outside the parenthesis
Example, (SO4)2-
Polyatomic Ions – Get List from class
• Most are anions
• 1 positive polyatomic ion  NH3+
(ammonium ion)
• Names must be memorized as they
can be different from the
combination of elements
Charges of Transition Metals (some 3A and
4A metals, too)
• Transition metals can have several different oxidation
numbers for transition metals (list on page 222)
• Electrons taken from s sublevel and/or d sublevel
• Always positive  cations
• For example, iron can be Fe2+ or Fe3+
• Roman numerals are used to tell you which oxidation
number an transition metal ion has
• Fe2+  iron (II)
• Fe3+  iron (III)
Zinc, Silver, Lead and Tin
• Zinc and Silver
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•
•
Transition metals
Do not require Roman numerals
Only have 1 oxidation number
Zn2+ and Ag+
• Lead and Tin
• p-block metals (group 4A)
• Require Roman numerals because each has more than 1 oxidation
number
• Sn2+, Sn4+, Pb2+, Pb4+
Naming ionic compounds with polyatomic
ions
• Binary (bi- means two) ionic compounds have only 2 types of
elements
• Ex: NaCl, CaF2____
, Al2O3 ____ ____
• If an ionic compound is not binary (more than 2 types of atoms), then
polyatomic ions must be involved
• Ex: NaNO3 
__ _ _
Na
NO3
sodium
nitrate
To Write the Names from the Formulas
with transition elements…
• Do reverse cross-over method
• SnS2
 Sn S2
 Sn2+ S1• If the charge on the ion that you know is not correct, then multiply
both ions by the same number to get the correct charge
• So Sn4+ must be the tin (IV) ion
 Sn2+ x (2) = +4  Sn4+
 name is tin (IV) sulfide.
S1- x (2) = -2  S2-