Binary Compounds of Cations with Variable Charges

Given Name, Write the Formula

Common Name System

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A binary compound is one made of two different elements. There can be one of each element such as in CuCl or FeO. There can also be several of each element such as Fe2O3 or CuBr2.

This lesson shows you how to write the formula of a binary compound when given the name using the common naming system. This means a cation of variable charge is involved. The four formulas above are all examples of this type. Important point to remember: the cations involved in this lesson have variable charges. The anions involved have only one charge.

Antoine Laurent Lavoisier (1743-94) reformed chemistry in the late 1700's with his publication of Méthode de nomenclature chimique in 1787 (along with three co-authors) and Traité élémentaire de Chimie in 1789. He is known as the "Father of Modern Chemistry."

Two typical names of chemicals up to this point in history are "foliated earth of tartar" and "phlogisticated vitriolic acid." There were hundreds of such names. One goal of the Méthode was to create chemical names based on the chemical composition.

Lavoisier's solution, which will be studied in this lesson, was to use different suffixes to indicate differences in composition. Specifically, the use of "-ous" and "-ic" will be studied.

Here is what the IUPAC currently says about this naming system: "The following systems are in use but not recommended: The system of indicating valence by means of the suffixes -ous and -ic added to the root of the name of the cation may be retained for elements exhibiting not more than two valences."

By the way, this picture of Lavoisier is a detail from a larger painting. In it, he is looking up toward his wife.

In everything that follows, remember this overall guiding principle: the total positive charge MUST equal the total negative charge.

All names such as "ferrous" or "plumbic" are given in the Nomenclature Data Sheet. This is what is handed out in the ChemTeam's classroom. Feel free to download it, clean it up in your word processor and use it. Print off a few extra to share with others. The ChemTeam thanks you.

In the past, some students have asked for a list of roots. Here is a small list.

Elementroot Elementroot
iron"ferr-" chromium"chrom-"
lead"plumb-" tin"stann-"
copper"cupr-" cobalt"cobalt-"
gold"aur-" manganese"mangan-"

Example #1: cuprous chloride

Step #1 - cuprous is the name of a very specific cation. It is Cu+ and nothing else.

I can see you saying to yourself "How in the world do I know that cuprous means Cu+?" Answer - you know by your studies which cation goes with which name. If you give your studies enough time, you will memorize all the names and charges, just like you have memorized many other things in your life.

Step #2 - chloride is the name of a specific anion. It is Cl¯.

Step #3 - remembering thatthe total charge of the formula must be zero, you write the formula CuCl.

Example #2: ferrous oxide

Ferrous means Fe2+.

Oxide means O2¯.

Following the usual rules, you write FeO for the formula.

Example #3: ferric sulfide

Ferric gives Fe3+.

Sulfide is S2¯.

The formula is Fe2S3

Keep the charge crossing technique in mind as you think about how this formula was made. Specifically, examine the aluminum oxide example.

Example #4: stannic phosphide

Stannic means Sn4+. Just like "apple" or "light bulb" mean specific things

Phosphide means P3¯.


Example #5: mercurous chloride

Mercurous means Hg22+

Chloride means Cl¯.


This formula is not reduced.

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Practice Problems

Write the correct formula for:

1) cupric phosphide

2) auric sulfide

3) manganous chloride

4) ferric bromide

5) mercurous oxide

6) aurous nitride

7) stannous fluoride

8) ferrous iodide

9) mercuric oxide

10) plumbous bromide Answers to Set One

Write the correct formula for:

11) cuprous fluoride

12) stannic sulfide

13) ferric sulfide

14) plumbous oxide

15) ferric chloride

16) stannic oxide

17) cuprous sulfide

18) mercurous chloride

19) cobaltic iodide

20) plumbic phosphide Answers to Set Two

Write the correct formula for:

21) ferrous nitride

22) stannous bromide

23) plumbous sulfide

24) cupric oxide

25) cuprous chloride

26) mercurous nitride (requires parenthesis)

27) mercuric sulfide

28) ferrous phosphide

29) plumbic nitride

30) cupric chloride Answers to Set Three

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