Nomenclature of Elements and Ionic Compounds

• Example: $\text{Cu}^{+}$ is the copper (I) ion, while $\text{Cu}^{2+}$ is the copper (II) ion.

Negative Ion Nomenclature

Negative ions, or anions, follow different naming conventions. Single-atom negative ions are named by taking the stem of the element's name and adding the suffix -ide.

| Element

• | | Bromine | $\text{Br}^{-}$ | Brom- | | | Chlorine | $\text{Cl}^{-}$ | Chlor- | | | Oxygen | $\text{O}^{2-}$ | Ox- | | | Sulfur | $\text{S}^{2-}$ | Sulf- | |

Polyatomic Ions

Polyatomic ions are groups of atoms that carry an overall charge and act as a single unit. Unlike single-atom ions, polyatomic ions have unique names that must be memorized, as there are very few predictable patterns.

Some patterns do exist, particularly for oxygen-containing ions. For halogens, the names follow a specific sequence based on the number of oxygen atoms: hypo-ite, -ite, -ate, and per-ate.

Exam Tip: When naming compounds containing polyatomic ions, treat the entire polyatomic group as a single unit. For example, in $\text{NaOH}$, the name is sodium hydroxide; you do not change the name of the hydroxide ion.

Binary Ionic Compounds

A binary ionic compound is composed of exactly two different elements: a metal and a nonmetal. The naming process depends on whether the metal involved has a fixed or variable charge.

Fixed Charge Metal Ions

There are 15 specific elements that are classified as fixed charge metal ions. These metals always carry the same charge regardless of the compound they form. Examples include:

• Group 1 metals: $\text{Li}^{+}$, $\text{Na}^{+}$, $\text{K}^{+}$, $\text{Rb}^{+}$, $\text{Cs}^{+}$
• Group 2 metals: $\text{Be}^{2+}$, $\text{Mg}^{2+}$, $\text{Ca}^{2+}$, $\text{Sr}^{2+}$, $\text{Ba}^{2+}$
• Others: $\text{Ag}^{+}$, $\text{Zn}^{2+}$, $\text{Cd}^{2+}$, $\text{Al}^{3+}$, $\text{Ga}^{3+}$

For these metals, the naming is straightforward: [Name of Metal] + [Name of Nonmetal with "-ide" suffix].

• Example: $\text{NaCl}$ is sodium chloride.

Variable Charge Metal Ions

Most other metals are variable charge metals, meaning they can exist in multiple oxidation states. When naming compounds with these metals, you must use one of two methods:

1. Roman Numeral Convention (Modern): Use the metal name followed by the charge in Roman numerals.
   • $\text{FeCl}_{2}$ is iron (II) chloride.
2. Systematic Suffixes (Older): Use the suffix -ous for the ion with the lower charge and -ic for the ion with the higher charge.
   • $\text{FeCl}_{2}$ is ferrous chloride.

| Element

• | | Iron (Fe) | $+2, +3$ | Ferr- | | | Copper (Cu) | $+1, +2$ | Cupr- | | | Lead (Pb) | $+2, +4$ | Plumb- | |

Summary of Naming Rules

To name any binary ionic compound, follow these steps:

1. Identify the metal (cation) and the nonmetal (anion).
2. Name the metal first. If it is a variable charge metal, add the charge in Roman numerals.
3. Name the nonmetal second. Change its ending to -ide.
4. Do not include the number of ions in the name. The ratio of ions is inferred from the chemical formula.

Note: While the name does not include numbers, you must be able to work backward from a name to a formula. For example, knowing that $\text{Fe}^{2+}$ and $\text{Cl}^{-}$ form a compound requires you to balance the charges to write $\text{FeCl}_{2}$.