Naming Inorganic Compounds

 

v     Ionic or Molecular? Before you name a compound you must decide whether of not the compound is ionic or molecular. The compound is ionic if the compound is a metal cation or polyatomic ion combined with a non-metal anion or polyatomic ion.  The compound is covalent (or molecular) if it is a combination of non-metals.

a Polyatomic Ions are ions formed from more than one element. The polyatomic ions you are responsible for include: ammonium (NH₄⁺); hydroxide (OH^-); acetate (CH₃CO₂^-); carbonate (CO₃^2-), bicarbonate (hydrogen carbonate) (HCO₃^-), nitrate (NO₃^-), nitrite (NO₂^-), phosphate (PO₄^3-), sulfate (SO₄^2-), and sulfite (SO₃^2-).  There are more polyatomic ions listed in your book in Table 2.5 on page 62.

 

Examples:

CaCl₂  - calcium is a metal (in group IIA) and chlorine is a non-metal (group VIIA). In this compound they exist as ions Ca²⁺ and Cl^-, and calcium chloride is ionic.

 

SO₂ - S, sulfur (group VIA) and O, oxygen (group VIA) are both non-metals; therefore sulfur dioxide is molecular.

 

(NH₄)₂SO₄ - NH₄⁺ is a polyatomic ion and SO₄^2- is a polyatomic ion; therefore, ammonium sulfate is ionic.

 

v     Binary Ionic Compounds

The names of all ionic compounds containing only two elements end in -ide.  The metal (or cation) is named after the element. The non-metal (or anion) has the stem of the element followed by -ide.

Stems of common elements:

      Oxygen -- Ox                           Nitrogen -- Nitr

      Chlorine -- Chlor                      Phosphorous -- Phosph

      Carbon -- Carb                        Fluorine -- Fluor

      Iodine -- Iod                            Bromine -- Brom

      Selenium -- Selen                     Sulfur -- Sulf

Examples:

      MgO - Magnesium Oxide

      K₂S - Potassium Sulfide

AlN - Aluminum Nitride

 

Note the subscripts. These are determined by looking at the oxidation state of the metal cation and non-metal anion. The overall oxidation state of a compound must be zero.

a Oxidation State (also called valence) - indicates the number of electrons removed or gained from the neutral atom to form the ion. See Tables 2.4 on page 61 in your book for common oxidation states of metals and nonmetals. Anions in group VII elements have a -1 charge, anions of Group VI elements have a -2 charge, and anions in group V elements have a -3 charge.) The periodic table is a good guide for the oxidation states of the main group elements.

K₂S - Since sulfur anion is in group VI, its anion has a -2 charge. K is in group I, so it has a +1 charge. In order for the compound to be neutral, 2 potassium ions must be part of the formula.

 

            Transition Metal Cations can exist in more than one oxidation state. Therefore, the oxidation state of the metal must be included in the name.

 

Examples:

FeO - Iron (II) Oxide

Fe₂O₃ - Iron(III) Oxide

 

l How do I know when to say Iron (II) and when to say Iron (III) in the above iron oxides? We look at the anion. In this case, oxygen is the non-metal anion. Oxygen is in Group VI and Group VI anions have a -2 charge. Compounds are neutral species, so the cation, in this case iron must have a charge such that the overall charge is zero.

In FeO   --  Let x = charge on iron, x + (-2) = 0 then x = 2 so we have iron (II).

In Fe₂O₃ -- Let x = charge on iron, 2x + 3(-2) = 0 then x = 3 so we have iron (III).

 

More Examples:

CuI  - copper (I) iodide

SnBr₄ - tin (IV) bromide

HgS - mercury (II) sulfide

 

v     Naming Ternary Ionic Compounds

Naming Ternary compounds is similar to naming binary compounds. Be alert for the polyatomic ions.

Examples:

NaHCO₃ - Sodium Hydrogen Carbonate (or Sodium Bicarbonate)

 

v     Naming Hydrates

Inorganic compounds often crystallize with water molecules. These molecules of water are noted in the name by using the word hydrate.  The number of water molecules is indicated by a prefix.  The prefixes used for naming compounds are:

Mono- 1                      Hepta - 7

Di-       2                      Octa  -             8

Tri-      3                      Nona - 9

Tetra-   4                      Deca - 10

Penta-  5                      Undeca - 11

Hexa-   6                      Dodeca - 12

 

Examples:

CuSO₄^.5H₂O -- Copper(II) Sulfate Pentahydrate

CrCl₃^.6H₂O --  Chromium(III) Chloride Hexahydrate

 

v     Naming Inorganic Molecular Compounds

The naming of molecular inorganic compounds is different from that of ionic compounds. Prefixes are used to indicate the number of atoms of an element present in a molecule.

Examples:

PCl₃ - Phosphorous Trichloride

SO₂ - Sulfur Dioxide

N₂O₅ - Dinitrogen Pentoxide

 

Usually if there is only one atom present we do not use a prefix. One exception is CO or carbon monoxide.

 

Practice:

1.      copper (I) oxide

2.      silver (I) nitrate

3.      potassium fluoride

4.      ammonium chloride

5.      aluminum hydroxide

6.      potassium nitrite

7.      arsenic trichloride

8.      diphosphorus pentoxide

9.      silicon dioxide

10.  magnesium nitride

 

1.      HgCl₂

2.      CaCO₃

3.      FeS

4.      SnO

5.      AsCl₅

6.      Li₃PO₄^. 3H₂O

7.      CoCl₃

8.      Be(OH)₂

9.      NaHCO₃

10.  K(CH₃CO₂)