Chapter 4: Unit 5. Nomenclature of Binary Ionic Compounds

Nomenclature of Binary Ionic Compounds

Name of monoatomic cations:

When main group metal loses electron(s) based on octet rule, it forms monoatomic cations. The charge of the metal is not required to include in the name because charge is fixed. Here are some examples of common monoatomic ions

Mg²⁺ : Magnesium ion

Al³⁺: Aluminum ion

Ba²⁺: Barium ion

Name of the monoatomic anions:

Some names of common monoatomic ions including polyatomic ions with end name -ide. Some common names are given below in the table.

Example: When Ba²⁺ combines with O^2- , total charge is neutralized by 1:1 ratio. So the formula of the compound is BaO.

In case of transition element, metal has a variable charge, use the overall anion charge to determine the charge on the cation. Then name the cation with charge using a roman numeral with parentheses. For example, in CuCl₂, charge of each chloride ion is -1. Therefore, total negative charge is -1*2 for two ions in the formula. In order to make total charge zero, the charge of Cu must be +2. The name of the compound Copper (II) Chloride.

Here are some other examples given below:

Common names have been traditionally used for transition metals but systematic names are accepted and used worldwide.

Ionic compounds are always named with the name of the cation first with cations having a fixed charge, the cations have the same name as the name of the original element.  The name of the anion usually ends with suffic -ide. It is derived from a single atom or -ate if it is polyatomic.

Example: When Ba²⁺ combines with O2- , total charge is neutralized by 1:1 ratio. So the formula of the compound is BaO.

Determination of charge in transition metal ionic compound:

Example: FeCl₃

Charge of the metal cation is determined with respect to anion’s charge.

In the above example Cl- has charge-1. Since there are total 3 Cl- ions are present in the compound, total negative charge is 3-. In an ionic compound total charge must be balanced. Therefore the charge of the metal cation is 3+

Name of the compound Iron(III) Chloride.

Another example: Co₂O₃

three oxide ions containing 2- each charge make total negative charge  -2*3= -6.

There are two metal Co to balance the total charge by +6.

So the charge of one Co metal is +6/2= +3.

The name of the compound Cobalt(III) Oxide.

An app is available for mobile devices with the name chemicals F& N  ( Formation and Nomenclature). You many practice nomenclature of ionic compound using this app.

Questions

Name each ionic compound a. FeCl₂, b) CoBr₃ c) Cus d) Cr₂S₃, d) Al₂O₃

Ans: a. Barium Chloride b. Cobalt(III) Bromide c. Copper(II) sulfide, d. Aluminum Oxide