Guide to Naming Ionic Compounds

Guide to Naming
Ionic Compounds
February 18
Naming Ions and Ionic Compounds
• Cations (+)
– The name of a cation is the same as the name of
the element
– Find name either on the periodic table or from
memory
– A few cations need Roman numerals with the
name
Cations that need Roman Numerals
• All d-block elements except Ag+, Zn2+, Cd2+
• Some p-block elements
Zn2+
Ag+ Cd2+
Roman Numerals
• I, II, III, IV, V, VI, VII, IX, X, etc.

Some cations need Roman numerals because they can
form more than one ion by losing different numbers of
valence electrons
• The numeral tells you the charge of the ion.
For example:
– Symbol
– Ti2+
– Ti4+
Cation name
titanium (II)
titanium (IV)
Exceptions
• All d-block elements need Roman numerals
except Ag+, Zn2+, Cd2+
– Silver, zinc, and cadmium will only form one ion. The
charge will always be the same for these three
cations.
• Symbol
– Ag+
– Zn2+
– Cd2+
Cation name
silver
zinc
cadmium
NOT: Silver (I)
NOT: Zinc (II)
NOT: Cadmium (II)
Examples: Name to Symbol
• Cation name
– Sodium
– Hydrogen
– Vanadium (III)
– Tin (II)
Symbol
Na+
H+
V3+
Sn2+
The Roman numeral tells
us the charge of the
vanadium and tin ions
All cations have
positive charges
We know the charge of
the sodium and hydrogen
cations by looking at a
periodic table
Note on Determining the Charge
• Depends on number of valence electrons
• How many electrons does the atom need to
gain or loose to reach a full valence shell?
– Will loose to reach 0 electrons or
– Will gain to reach 8 electrons
– If it looses electrons, the ion is positive
– If it gains electrons, the ion is negative
Another way to think about ionic charge…
Examples: Symbol to Name
• Symbol
– Sr2+
– Cd2+
– Cu2+
– Pb3+
– Pb2+
– K+
Cation name
Strontium
Cadmium
Copper (II)
Lead (III)
Lead (II)
Potassium
Sr2+ and K+ do not
need Roman numerals
because they are in
the s-block
Cadmium does not
need a Roman
numeral because it is
one of the three dblock exceptions
The charge of the ion symbol tells us what Roman numeral to
write in the name. Copper and lead need Roman numerals
because they are found in the d-block and lower-left p-block and
form more than one
ion.
Naming Ions and Ionic Compounds
• Anions (-)
– The name of a anion is similar to the name of the
element
• Find name either the periodic table or from memory
• Drop the ending of the element name
• Add –ide to the stem
– NOTE: If the anion’s name ends in –ide and is NOT
cyanide (CN-), hydroxide (OH-), or peroxide (O22-),
it will be an ion of an element you find on the
periodic table
Examples: Name to Symbol
• Cation name
– Bromide
– Oxide
– Nitride
All the names end in –ide:
- Bromine  bromide
- Oxygen  Oxide
- Nitrogen  Nitride
Symbol
BrO2N3-
All anions have
negative charges
We know the charge of
the anions by looking at a
periodic table
Another way to think about ionic charge…
Examples: Symbol to Name
• Symbol
– S2– Cl– P3-
Element name
sulfur
chlorine
phosphorous
Anion name
Sulfide
Chloride
Phosphide
Polyatomic Ions
• A molecule with a charge
• You will need to memorize the names
• They behave just like monotomic cations and
anions
Examples: Name to Formula
• Ion name
– Oxalate
– Chlorate
– Acetate
– Ammonium NH4+
Formula
C2O42ClO3CH3COO-
Examples: Formula to Name
• Ion name
– O22– CH3COO– Cr2O72– AsO43– MnO4-
Formula
Peroxide
Acetate
Dichromate
Arsenate
Permanganate
Helpful Tip 1: Hints in names
• Look for clues in the polyatomic ion names
• Example:
 Cr2O72Dichromate
- Chromate sounds like chromium
- Di means two
- Dichromate has two chromiums in it
Helpful Tip 2: -ate vs. –ite
• If two similar ions have names that end in
–ate and –ite, -ate will have more oxygen
– ClO3Chlorate
3 oxygens
– ClO2Chlorite
2 oxygens
– NO3Nitrate
3 oxygens
– NO2Nitrite
2 oxygens
– SO42Sulfate
4 oxygens
– SO32Sulfite
3 oxygens
Helpful Tip 3: Per- and Hypo• Per-: 1 more oxygen, same charge
• Hypo-: 1 less oxygen, same charge
– ClO4– ClO3– ClO2– ClO-
Perchlorate
Chlorate
Chlorite
Hypochlorite
4 oxygens
3 oxygens
2 oxygens
1 oxygen