Naming Ionic Compounds and Acids: Systematic and Common Approaches

Objectives and Overview

Introduction to Ionic Compound and Acid Nomenclature

This section covers the systematic and common naming conventions for ionic compounds and acids, focusing on compounds with metals of constant and variable charge, polyatomic ions, and acids containing oxyanions. Mastery of these topics is essential for understanding chemical formulas and communication in chemistry.

• Distinguish between common and systematic names for compounds

• Name binary ionic compounds with metals forming one or multiple types of ions

• Name compounds containing polyatomic ions

• Name binary acids and acids containing oxyanions ending in -ate or -ite

Ionic Compounds

Definition and Types of Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between a metal and a nonmetal. The metal loses electrons to become a positively charged cation, while the nonmetal gains electrons to become a negatively charged anion.

• Type 1 Ionic Compounds: Metals with constant (invariant) charge, typically main group elements (e.g., Na+, Ba2+).

• Type 2 Ionic Compounds: Metals with variable charge, usually transition metals (e.g., Fe2+, Fe3+).

Metals with Invariant Charge

Certain metals always form ions with the same charge, regardless of the compound. These are typically found in Groups 1A, 2A, and some in 3A of the periodic table.

• Examples: Sodium (Na+), Barium (Ba2+), Aluminum (Al3+)

• These metals give up electrons to form cations with a fixed oxidation state.

Table: Metals with Invariant Charge

Element	Symbol	Common Charge
Sodium	Na	+1
Barium	Ba	+2
Aluminum	Al	+3
Zinc	Zn	+2
Silver	Ag	+1
Scandium	Sc	+3

Binary Ionic Compounds

Definition and Naming Rules

Binary ionic compounds contain only two different elements: a metal and a nonmetal. If the metal forms only one type of ion, its charge does not need to be specified in the name.

• Naming format: Name of cation (metal) + base name of anion (nonmetal) + -ide suffix

Examples:

• NaCl: Sodium (Na) + Chlorine (Cl) → Sodium Chloride

• Al2O3: Aluminum (Al) + Oxygen (O) → Aluminum Oxide

Practice: Naming Binary Ionic Compounds

• MgCl2: Magnesium Chloride

• Li3P: Lithium Phosphide

• KBr: Potassium Bromide

• Na2S: Sodium Sulfide

Common Anions: Names and Symbols

Table: Common Anions and Their Naming Conventions

This table summarizes the base names and anion names for frequently encountered nonmetal ions.

Symbol for Ion	Base Name	Anion Name
F-	fluor-	fluoride
Cl-	chlor-	chloride
Br-	brom-	bromide
I-	iod-	iodide
O2-	ox-	oxide
S2-	sulf-	sulfide
N3-	nitr-	nitride

Ionic Compounds with Metals of Variable Charge

Naming Rules for Variable Charge Metals

Transition metals and some other metals can form ions with different charges. The charge must be specified in the compound's name using Roman numerals in parentheses.

• Exceptions: Zinc, Silver, and Scandium always have fixed charges and do not require Roman numerals.

• Naming format: Name of metal + (Roman numeral for charge) + base name of anion + -ide

Example:

• FeCl3: Iron (III) Chloride ($Fe^{3+}$ and $Cl^-$)

• Cu2O: Copper (I) Oxide ($Cu^+$ and $O^{2-}$)

Determining the Charge from the Formula

• The total positive and negative charges in the formula must sum to zero.

• For FeCl3: 3 chlorines ($3 imes -1 = -3$), so iron must be $+3$.

Ionic Compounds with Polyatomic Ions

Naming Compounds with Polyatomic Ions

Polyatomic ions are groups of atoms that carry a charge and act as a single unit in compounds. The naming procedure is similar to binary ionic compounds, but the name of the polyatomic ion is used directly.

• Examples:

  • Fe(NO3)2: Iron (II) Nitrate

  • NH4NO3: Ammonium Nitrate

Oxyanions and Their Acids

Oxyanions: Naming and Series

Oxyanions are polyatomic anions containing oxygen. Their names depend on the number of oxygen atoms present.

• If there are two ions in the series:

  • More oxygen: -ate ending (e.g., nitrate, sulfate)

  • Fewer oxygen: -ite ending (e.g., nitrite, sulfite)

• If there are more than two ions:

  • Hypo- prefix: least oxygen

  • Per- prefix: most oxygen

Examples:

• NO3-: Nitrate

• NO2-: Nitrite

• SO42-: Sulfate

• SO32-: Sulfite

Naming Acids Derived from Oxyanions

• Acids with -ate oxyanions: Replace -ate with -ic acid (e.g., HNO3: Nitric acid)

• Acids with -ite oxyanions: Replace -ite with -ous acid (e.g., HNO2: Nitrous acid)

Summary Table: Oxyanion Series and Acid Names

Oxyanion	Formula	Acid Name
Nitrate	NO3-	Nitric acid (HNO3)
Nitrite	NO2-	Nitrous acid (HNO2)
Sulfate	SO42-	Sulfuric acid (H2SO4)
Sulfite	SO32-	Sulfurous acid (H2SO3)

Key Equations and Concepts

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

• General formula for binary ionic compounds: $\text{Metal}^{n+} + \text{Nonmetal}^{m-} \rightarrow \text{Metal}_x\text{Nonmetal}_y$ where $x$ and $y$ are chosen to balance the charges.

Additional info:

• Polyatomic ions such as ammonium ($NH_4^+$), nitrate ($NO_3^-$), sulfate ($SO_4^{2-}$), and phosphate ($PO_4^{3-}$) are commonly encountered in introductory chemistry.

• Binary acids (e.g., HCl, HF) are named as "hydro-" + base name of nonmetal + "-ic acid" (e.g., hydrochloric acid).