Nomenclature of Inorganic Compounds

Common and Systematic Names

Nomenclature in chemistry refers to the system of naming chemical substances. Compounds often have both common names (arbitrary, based on properties or history) and systematic names (precisely describing chemical composition).

• Common Name: Informal, may relate to physical or chemical properties (e.g., "table salt" for NaCl).

• Systematic Name: Follows IUPAC rules, describes the exact chemical formula (e.g., "sodium chloride" for NaCl).

• Example: CaCO3 is commonly called "limestone" and systematically named "calcium carbonate."

Elements and Molecules

Diatomic and Polyatomic Molecules

Some elements do not exist as single atoms in nature; instead, they form molecules with two or more atoms.

• Diatomic molecules: Consist of two atoms bonded together (e.g., H2, O2, N2).

• Polyatomic molecules: Contain more than two atoms (e.g., P4, S8).

Formation and Naming of Ions

Forming Cations

Metals tend to lose electrons to achieve stability, forming positively charged ions called cations.

• Cation: An ion with a positive charge due to loss of electrons.

• Example: (potassium atom forms potassium ion).

Naming Cations

Cations are named after their parent atoms.

Forming Anions

Nonmetals gain electrons to become stable, forming negatively charged ions called anions.

• Anion: An ion with a negative charge due to gain of electrons.

• Example: (chlorine atom forms chloride ion).

Naming Anions

Monatomic anions use the stem of the element’s name with the ending changed to -ide.

Ion Charges and the Periodic Table

The charge of ions depends on their position in the periodic table. Metals on the left form only one ion, while many transition metals form multiple ions. The charge of a nonmetal is calculated as group number minus 8.

Ionic Compounds

Properties and Structure

Ionic compounds are formed by the electrostatic attraction between cations and anions. Their formulas represent the simplest whole-number ratio of each element.

• Solid at room temperature

• Conduct electricity when molten

• Example: NaCl (sodium chloride)

Writing Formulas for Ionic Compounds

To write the formula for an ionic compound:

1. Write the formula for the metal ion followed by the nonmetal ion.

2. Combine the smallest numbers of each ion needed to give a charge sum equal to zero.

3. Write the formula as the symbol for the metal and nonmetal, each followed by a subscript if needed.

• Example:

• Example:

• Example:

Naming Binary Ionic Compounds

Compounds with Metals Forming One Type of Cation

Binary ionic compounds contain only two elements: a metal and a nonmetal. For metals that form only one type of cation:

1. Write the name of the cation.

2. Write the name of the anion with the -ide ending.

• Example: is "aluminum fluoride"

• Example: is "potassium chloride"

Compounds with Metals Forming Multiple Types of Cations

For metals that can form more than one type of cation (often transition metals), the Stock System is used:

1. Name the cation with a Roman numeral indicating its charge.

2. Name the anion with the -ide ending.

• Example: is "iron(III) chloride"

• Example: is "copper(II) oxide"

Classic System

Some metals use Latin names with -ous and -ic suffixes to indicate lower and higher charges, respectively.

• Example: is "ferrous"; is "ferric"

• Example: is "stannous fluoride"

Naming Binary Molecular Compounds

Rules and Prefixes

Binary molecular compounds contain two nonmetals or a nonmetal and a metalloid. Prefixes indicate the number of atoms:

• Example: is "carbon monoxide"; is "carbon dioxide"

• Example: is "sulfur hexafluoride"

Acids Derived from Binary Compounds

Naming Binary Acids

Acid formulas begin with hydrogen. For binary acids in aqueous solution:

1. Write the prefix hydro- followed by the stem of the second element.

2. Add the suffix -ic and the word "acid."

• Example: (aq) is "hydrochloric acid"

• Example: (aq) is "hydrofluoric acid"

Polyatomic Ions

Definition and Examples

A polyatomic ion contains two or more elements bonded together, carrying a net charge.

• Many polyatomic ions containing oxygen are called oxy-anions and have names ending in -ate or -ite.

• -ate: More oxygen atoms (e.g., sulfate SO42-)

• -ite: One less oxygen atom (e.g., sulfite SO32-)

• Prefixes per- and hypo- indicate more or fewer oxygens, respectively.

• Some polyatomic ions end in -ide (e.g., hydroxide OH-, cyanide CN-).

• Only one common positive polyatomic ion: ammonium NH4+.

Writing Formulas with Polyatomic Ions

Parentheses are used around polyatomic ions when a subscript is needed to balance the charge.

• Example:

• Example:

Naming Compounds Containing Polyatomic Ions

To name these compounds:

1. Write the name of the cation.

2. Write the name of the anion.

• Example: is "ammonium nitrate"

• Example: is "lead(II) acetate"

Oxy-Acids

Naming Oxy-Acids

Oxy-acids are neutral compounds beginning with H and ending with an oxygen-containing polyatomic ion.

• If the polyatomic ion ends in -ate, the acid name ends in -ic acid.

• If the polyatomic ion ends in -ite, the acid name ends in -ous acid.

• Example: (sulfuric acid) from sulfate

• Example: (sulfurous acid) from sulfite

Comparison of Acid and Anion Names

Acids and their corresponding anions are systematically related in nomenclature.

Summary of Naming Binary and Polyatomic Compounds

Flow Diagrams for Naming Compounds

Flow diagrams help organize the rules for naming binary and polyatomic compounds.