Nomenclature of Inorganic Compounds: Study Notes and Practice

Nomenclature of Inorganic Compounds

Introduction

Chemical nomenclature is the systematic method of naming chemical compounds. Mastery of nomenclature is essential for clear communication in chemistry, especially when dealing with ionic, covalent, and acid compounds. This guide summarizes the rules and provides examples for naming and writing formulas for various classes of inorganic compounds.

Simple Ionic Compounds

Definition and Naming Rules

• Simple ionic compounds consist of a metal cation and a nonmetal anion.

• The cation (metal) is named first, followed by the anion (nonmetal) with its ending changed to -ide.

• Metals in Groups 1 and 2, along with aluminum, zinc, and silver, have only one possible charge and do not require Roman numerals.

Examples

• Rb3PO4: Rubidium phosphate

• BaCl2: Barium chloride

• MgSO4: Magnesium sulfate

• SrF2: Strontium fluoride

• MgBr2: Magnesium bromide

Ionic Compounds Containing Transition Metals

Definition and Naming Rules

• Transition metals can have multiple possible charges.

• The charge of the metal is indicated by a Roman numeral in parentheses after the metal's name.

• The anion is named as in simple ionic compounds.

Examples

• PtBr2: Platinum(II) bromide

• V2O5: Vanadium(V) oxide

• FeCl3: Iron(III) chloride

• Cu2O: Copper(I) oxide

• CoF2: Cobalt(II) fluoride

Ionic Compounds Containing Polyatomic Ions

Definition and Naming Rules

• Polyatomic ions are charged groups of covalently bonded atoms that act as a single ion.

• Common polyatomic ions include nitrate (NO3-), sulfate (SO42-), phosphate (PO43-), and ammonium (NH4+).

• Name the cation first, then the polyatomic anion.

Examples

• Na2SO4: Sodium sulfate

• Mg(NO3)2: Magnesium nitrate

• NH4ClO4: Ammonium perchlorate

• CaCO3: Calcium carbonate

• K2Cr2O7: Potassium dichromate

Covalent (Molecular) Compounds

Definition and Naming Rules

• Covalent compounds are formed between two nonmetals.

• Prefixes are used to indicate the number of each atom (mono-, di-, tri-, tetra-, penta-, etc.).

• The first element keeps its name; the second element ends with -ide.

• The prefix 'mono-' is usually omitted for the first element.

Examples

• CS2: Carbon disulfide

• CO: Carbon monoxide

• SF4: Sulfur tetrafluoride

• N2O5: Dinitrogen pentoxide

• BF3: Boron trifluoride

Acids

Definition and Naming Rules

• Acids are compounds that release H+ ions in water.

• If the anion ends in -ide, the acid name begins with hydro- and ends with -ic acid.

• If the anion ends in -ate, the acid name ends with -ic acid.

• If the anion ends in -ite, the acid name ends with -ous acid.

Examples

• HCl: Hydrochloric acid

• HNO3: Nitric acid

• H2SO4: Sulfuric acid

• H2SO3: Sulfurous acid

• HClO4: Perchloric acid

Writing Formulas from Names

General Approach

• Identify the cation and anion (including their charges).

• Balance the total positive and negative charges to write the correct formula.

• For acids, use the appropriate number of H+ ions to balance the anion's charge.

Examples

• Hydrochloric acid: HCl

• Mercury(II) sulfide: HgS

• Iron(III) carbonate: Fe2(CO3)3

• Ammonium acetate: NH4C2H3O2

• Magnesium hydrogen phosphate: MgHPO4

Common Polyatomic Ions

Table: Names and Formulas

Name	Formula
Ammonium	NH4+
Nitrate	NO3-
Sulfate	SO42-
Phosphate	PO43-
Hydroxide	OH-
Carbonate	CO32-
Perchlorate	ClO4-
Permanganate	MnO4-

Summary Table: Types of Compounds and Naming Patterns

Type	Example Formula	Naming Pattern
Simple Ionic	NaCl	Metal + Nonmetal(-ide)
Transition Metal Ionic	FeCl3	Metal(Roman numeral) + Nonmetal(-ide)
Polyatomic Ionic	NaNO3	Metal + Polyatomic Ion
Covalent	CO2	Prefix + Nonmetal + Prefix + Nonmetal(-ide)
Acid	H2SO4	Based on anion: -ide → hydro-...-ic acid; -ate → ...-ic acid; -ite → ...-ous acid

Practice Problems

Sample Questions

• Write the name for the following compound: K2SO4

• Write the formula for calcium nitrate.

• Name the acid: HNO2

• Write the formula for copper(II) sulfate.

Answers

• K2SO4: Potassium sulfate

• Calcium nitrate: Ca(NO3)2

• HNO2: Nitrous acid

• Copper(II) sulfate: CuSO4

Key Equations and Concepts

• Charge balance for ionic compounds: $\text{Total positive charge} + \text{Total negative charge} = 0$

• Prefixes for covalent compounds: $\text{mono-} = 1, \text{di-} = 2, \text{tri-} = 3, \text{tetra-} = 4, \text{penta-} = 5, \text{hexa-} = 6$

Additional info: This guide is based on a nomenclature homework key and covers the essential rules and examples for naming and writing formulas for inorganic compounds, as required in General Chemistry.