CHM 101 - LECTURE NOTES

CHM 101 GENERAL CHEMISTRY

FALL QUARTER 2008

Section 2

Lecture Notes – 10/8/2008

(last revised: 10/7/08)

2.8 Naming Simple Chemical Compounds

Most elements have symbols that are directly constructed from the names. For example:

Symbol is First Letter of Name

Symbol is First Two Letters of Name

Symbol is First Plus Another Letter of Name

Some elements have symbols that are based on their original names instead of their current names. These require memorization:

Naming of Binary Ionic Compounds: These are compounds containing monatomic ions of two elements.

One of the components is a monatomic anion. The names of monatomic anions are based on the names of the elements, but the endings are changed to “-ide.” Note that the ions with -1 charges are all from Group 17 (except for hydride); those with -2 charges are from Group 16; and those with -3 charges are from Group 15 of the periodic table.
And, as an aid to learning, let’s mark our periodic tables to show the positions of each element that forms monatomic ions, with different colors for anions, Type I cations, and Type II cations.

The other component is a monatomic cation. There are two types of these ions. We consider first Type I, where the element forms only one kind of ion. Note that all of the cations from elements in Group 1 have +1 charges and that all the cations of Group 2 elements have +2 charges. Note also that the cations have names that are identical to the names of the elements.

Let’s pause here and name some Binary Ionic Compounds of Type I. Here are the rules:

There is always one kind of monatomic cation and one kind of monatomic anion.
The name of the cation comes first. The name of the anion comes second.
The net charge on an ionic compound is 0. This means that the numbers of ions of each type must be chosen so that the charges balance.
Some examples:

Now we consider Type II cations. These differ from Type I in that the metals that form them by ionization can form more than one kind of ion. Take iron (Fe) for example. There are two kinds of iron chloride:

The rules for naming Type II Binary Ionic Compounds are the same as for Type I, except that there is one additional rule. We use a roman numeral in the chemical name to indicate the charge on the cation.
Here is a list of common Type II cations. You need to memorize which charges go with which elements. Note also that mercury (I) always occurs as the diatomic ion, Hg₂²⁺.

The hard part is memorizing the formulas, the charges, and the names of the common polyatomic ions, but such memorization is absolutely necessary. Here is the list: