Language of Chemistry: Classification and Nomenclature

Overview of Inorganic Compounds and Acids

Inorganic compounds are classified based on their composition and bonding. Most inorganic compounds do not contain carbon, with exceptions such as carbon dioxide and carbonates. The International Union of Pure and Applied Chemistry (IUPAC) sets the rules for naming these compounds, ensuring systematic and universal nomenclature.

Classes of Inorganic Compounds

There are five common classes of inorganic compounds:

• Binary Ionic Compounds: Composed of a metal and a nonmetal (e.g., NaCl, CaO).

• Ternary Ionic Compounds: Contain a metal, a nonmetal, and oxygen (e.g., KNO3, CaCO3).

• Binary Molecular Compounds: Composed of two nonmetals (e.g., NH3, SO2).

• Binary Acids: Aqueous solutions of hydrogen and a nonmetal (e.g., HCl(aq)).

• Ternary Oxyacids: Aqueous solutions of hydrogen, oxygen, and another nonmetal (e.g., HNO3(aq)).

Classification of Ions

Types of Ions

An ion is an atom or group of atoms with a charge. Ions are classified as:

• Cations: Positively charged ions (e.g., Na+, NH4+).

• Anions: Negatively charged ions (e.g., Cl–, SO42–).

• Monoatomic: Single atom ions (e.g., Na+, Cl–).

• Polyatomic: Group of atoms with a charge (e.g., NH4+, CO32–).

Common Monoatomic Anions

Monoatomic anions are named by adding the suffix -ide to the root name of the element.

Predicting Charges of Monoatomic Ions

The charge of a metal ion from representative elements (A groups) is equal to the family number. For anions, the charge is the family number minus eight.

• Formula:

Common Polyatomic Ions

Polyatomic ions often contain oxygen and are called oxyanions. The suffix -ate indicates more oxygen atoms, while -ite indicates fewer. Some exceptions use -ide (e.g., hydroxide, cyanide).

Writing Chemical Formulas

Formulas of Ionic Compounds

An ionic compound is composed of positive and negative ions. The formula unit is neutral, so the total positive charge must equal the total negative charge.

• If charges are equal: one of each ion (e.g., Ca2+ and O2– form CaO).

• If charges are not equal: balance charges with subscripts (e.g., Ba2+ and Cl– form BaCl2).

Formulas with Polyatomic Ions

Follow the same rules as binary ionic compounds. If more than one polyatomic ion is needed, use parentheses (e.g., (NH4)2SO4).

Naming Ionic and Molecular Compounds

Naming Binary Ionic Compounds

Combine the cation and anion names, dropping the word "ion." The cation is named first, followed by the anion with the suffix -ide.

Naming Binary Molecular Compounds

Binary molecular compounds are composed of two nonmetals. The first element is named first, and the second element has the suffix -ide. The number of atoms is indicated by Greek prefixes.

Example: Naming P4S3

P4S3 is named tetraphosphorus trisulfide, using the prefixes tetra– and tri–.

Naming Acids

Binary Acids

A binary acid is an aqueous solution of hydrogen and a nonmetal. The formula begins with H. Binary acids are named using the prefix hydro– and the suffix -ic acid (e.g., HF(aq) is hydrofluoric acid).

Ternary Oxyacids

Ternary oxyacids are aqueous solutions of hydrogen and an oxyanion. If the acid is derived from an oxyanion ending in -ate, the suffix is changed to -ic acid (e.g., HNO3(aq) is nitric acid). If derived from -ite, the suffix is changed to -ous acid (e.g., HNO2(aq) is nitrous acid).

Summary of Key Points

• Most inorganic compounds do not contain carbon.

• Binary ionic compounds: metal + nonmetal.

• Ternary ionic compounds: metal + nonmetal + oxygen.

• Binary molecular compounds: two nonmetals.

• Acids: hydrogen + nonmetal or oxyanion.

• Cations: element name + "ion"; variable charge indicated by Roman numerals.

• Ionic compounds: cation first, anion second, anion ends with -ide.

• Molecular compounds: Greek prefixes indicate number of atoms.

• Binary acids: hydro– + element stem + -ic acid.

• Ternary oxyacids: -ate becomes -ic acid, -ite becomes -ous acid.