http://www.ck12.org Chapter 7. Chemical Nomenclature
Notice in the table above (Table7.2) that there are three cations whose names do not include a Roman numeral.
Silver, cadmium, and zinc only form one common type of ion, so the charges on ions of these elements are considered
to be implied by the name (1+ for silver and 2+ for zinc and cadmium). By convention, the Stock system is not
used for these elements, and their cations are named in the same way as those of the representative elements. The
mercury(I) ion is a special case that consists of a pair of mercury atoms bonded together. The overall ion has a
charge of 2+, so each mercury ion can be thought of as carrying a 1+ charge. In some instances, charges greater than
4+ are seen, but because these are less common, they are not included in the table.
There is an older system for naming some of these cations that is still occasionally used. The Latin root of the metal
name is written with one of two suffixes: (1)–icfor the ion with a higher charge, and (2)–ousfor the ion with a
lower charge. For example, the Latin name for iron is ferrum, so the Fe^3 +ion is called the ferric ion, and the Fe^2 +
ion is called the ferrous ion. The primary disadvantage of this system is that the suffixes do not tell you exactly
what the charge is for a given ion. For copper, the two most common charges are 1+ and 2+, so Cu^2 +is called the
cupric ion and Cu+is the cuprous ion. The Stock system is a much more informative system and will be used as the
primary method for naming transition metal compounds throughout this book.
Binary Ionic Compounds
Abinary ionic compoundis a compound made by combining monatomic metal cations with monatomic nonmetal
anions.
Naming Binary Ionic Compounds
When given the formula of a chemical compound, you must first decide what kind of compound it is before you can
determine how it should be named. A binary ionic compound will contain one metallic element and one nonmetallic
element. By convention, the metal is generally written before the nonmetal in the chemical formula for this type
of compound. To name a binary ionic compound, simply write the name of the cation followed by the name of the
anion. Note that subscripts in the formula do not affect the name. Below are three examples (Table7.3).
TABLE7.3: Examples of Binary Ionic Compounds
Formula Name
KF potassium fluoride
Na 3 N sodium nitride
Ca 3 P 2 calcium phosphideNotice that in each of the formulas above, the overall charge of the compound is zero. Since potassium ions (K+)
and fluoride ions (F−) have charges of equal magnitude, a neutral compound is formed when combining them in a
1:1 ratio, resulting in a formula that contains one of each ion. This would also be the case for a compound such as
MgS, which is composed of Mg^2 +and S^2 −. For sodium nitride, the sodium ion (Na+) has a charge of 1+, while the
nitride ion (N^3 −) has a charge of 3-. In order to make a neutral compound, three of the 1+ sodium ions are needed
to balance out each 3- nitride ion. This is reflected in the chemical formula by giving Na a subscript of 3. Calcium
phosphide is composed of calcium ions (Ca^2 +) and phosphide ions (P^3 −). Determining the necessary ratio for ions
whose charges both have magnitudes greater than 1 can sometimes be made easier by looking for the least common
multiple of the two charges. In this case, the least common multiple of 2 and 3 is 6. To make the compound neutral,
three calcium ions (with a total charge of 6+) should be combined with two phosphide ions (with a total charge of
6 −). The Ca is given a subscript of 3, while the P is given a subscript of 2.
Practice naming binary ionic compounds with this short crossword puzzle: https://sites.google.com/site/pattihowel