Guide to Naming Ionic Compounds

February 18

• 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

Naming Ions and Ionic Compounds

• All d-block elements except Ag+, Zn2+, Cd2+

• Some p-block elements

Cations that need Roman Numerals

Zn2+

Ag+ Cd2+

• 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 Cation name– Ti2+ titanium (II)– Ti4+ titanium (IV)

Roman Numerals

• 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 Cation name– Ag+ silver NOT: Silver (I)– Zn2+ zinc NOT: Zinc (II)– Cd2+ cadmium NOT: Cadmium (II)

Exceptions

• Cation name Symbol– Sodium Na+

–Hydrogen H+

–Vanadium (III) V3+

– Tin (II) Sn2+

Examples: Name to SymbolAll cations have positive charges

The Roman numeral tells us the charge of the vanadium and tin ions

We know the charge of the sodium and hydrogen cations by looking at a periodic table

• 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

Note on Determining the Charge

Another way to think about ionic charge…

• Symbol Cation name– Sr2+ Strontium–Cd2+ Cadmium–Cu2+ Copper (II)–Pb3+ Lead (III)–Pb2+ Lead (II)–K+ Potassium

Examples: Symbol to NameSr2+ and K+ do not need Roman numerals because they are in the s-block

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.

Cadmium does not need a Roman numeral because it is one of the three d-block exceptions

• 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 (O2

2-), it will be an ion of an element you find on the periodic table

Naming Ions and Ionic Compounds

• Cation name Symbol–Bromide Br-

–Oxide O2-

–Nitride N3-

Examples: Name to SymbolAll anions have negative charges

All the names end in –ide:- Bromine bromide- Oxygen Oxide- Nitrogen Nitride

We know the charge of the anions by looking at a periodic table

Another way to think about ionic charge…

• Symbol Element name Anion name– S2- sulfur Sulfide–Cl- chlorine Chloride–P3- phosphorous Phosphide

Examples: Symbol to Name

Polyatomic Ions

• A molecule with a charge• You will need to memorize the names• They behave just like monotomic cations and

anions

• Ion name Formula–Oxalate C2O4

2-

–Chlorate ClO3-

–Acetate CH3COO-

–Ammonium NH4+

Examples: Name to Formula

• Ion name Formula–O2

2- Peroxide

–CH3COO- Acetate

–Cr2O72- Dichromate

–AsO43- Arsenate

–MnO4- Permanganate

Examples: Formula to Name

• Look for clues in the polyatomic ion names• Example: Cr2O7

2- Dichromate

Helpful Tip 1: Hints in names

- Chromate sounds like chromium- Di means two- Dichromate has two chromiums in it

• If two similar ions have names that end in –ate and –ite, -ate will have more oxygen –ClO3

- Chlorate 3 oxygens

–ClO2- Chlorite 2 oxygens

–NO3- Nitrate 3 oxygens

–NO2- Nitrite 2 oxygens

– SO42- Sulfate 4 oxygens

– SO32- Sulfite 3 oxygens

Helpful Tip 2: -ate vs. –ite

• Per-: 1 more oxygen, same charge• Hypo-: 1 less oxygen, same charge

–ClO4- Perchlorate 4 oxygens

–ClO3- Chlorate 3 oxygens

–ClO2- Chlorite 2 oxygens

–ClO- Hypochlorite 1 oxygen

Helpful Tip 3: Per- and Hypo-