Classification and Naming of Inorganic Compounds and Acids

Language of Chemistry: Classification and Naming of Inorganic Compounds

Classification of Inorganic Compounds

Inorganic compounds are generally defined as compounds that do not contain carbon, with some exceptions such as CO2 (carbon dioxide), CO32- (carbonate), and HCO3- (hydrogen carbonate). These compounds are classified into five main groups based on their composition:

• Binary Ionic Compounds: Contain one metal and one nonmetal. Example: KCl, AlCl3.

• Ternary Ionic Compounds: Contain three elements, including at least one metal and one nonmetal. Example: KNO3, Al(NO3)2.

• Binary Molecular Compounds: Composed of two nonmetals. Example: H2O, NH3.

• Binary Acids: Aqueous solutions of compounds containing hydrogen and a nonmetal. Formulas begin with H. Example: HCl(aq), H2S(aq).

• Ternary Oxyacids: Aqueous solutions containing hydrogen, a nonmetal, and oxygen. Example: HNO3(aq), H2SO4(aq).

Aqueous solution refers to a compound dissolved in water (H2O).

Classification of Ions

Ions are charged particles formed when atoms gain or lose electrons. They are classified as:

• Cation: A positive ion (e.g., Na+, Mg2+).

• Anion: A negative ion (e.g., Cl-, O2-).

• Monatomic Ion: A single atom with a charge (e.g., Cl-, Mg2+).

• Polyatomic Ion: A group of atoms bonded together with an overall charge (e.g., SO42-, CO32-).

Monatomic Ions

Naming Monatomic Ions

The names of most monatomic cations are derived from the parent metal. For transition metals with multiple possible charges, two naming systems are used:

• Stock System: Indicates the charge with Roman numerals in parentheses. Example: Cu2+ is copper(II) ion.

• Latin System: Uses the suffixes -ous (lower charge) and -ic (higher charge) with the Latin name. Example: Cu2+ is cupric ion.

Monatomic anions are named by adding the suffix -ide to the nonmetal stem. Examples: Cl- is chloride ion, O2- is oxide ion.

Common Monatomic Ions

Cation	Name
Na+	Sodium ion
Mg2+	Magnesium ion
Fe2+	Iron(II) ion / ferrous ion
Fe3+	Iron(III) ion / ferric ion
Cu2+	Copper(II) ion / cupric ion
Additional info: See textbook Table 6.1 for more examples.

Anion	Name
Cl-	Chloride ion
O2-	Oxide ion
S2-	Sulfide ion
Additional info: See textbook Table 6.2 for more examples.

Polyatomic Ions

Naming Polyatomic Ions

Polyatomic ions are groups of atoms with a charge. Most polyatomic anions contain oxygen and are called oxyanions. Their names typically end in -ate (more oxygen) or -ite (less oxygen). Some exceptions use -ide.

• SO42-: Sulfate ion

• SO32-: Sulfite ion (one less oxygen than sulfate)

• ClO3-: Chlorate ion

• ClO2-: Chlorite ion

• CN-: Cyanide ion (exception, ends in -ide)

• OH-: Hydroxide ion (exception, ends in -ide)

• NH4+: Ammonium ion (cation)

Common Polyatomic Ions

Ion	Name
NH4+	Ammonium ion
C2H3O2-	Acetate ion
CO32-	Carbonate ion
NO3-	Nitrate ion
NO2-	Nitrite ion
SO42-	Sulfate ion
SO32-	Sulfite ion
PO43-	Phosphate ion
ClO4-	Perchlorate ion
MnO4-	Permanganate ion
CrO42-	Chromate ion
Cr2O72-	Dichromate ion
HCO3-	Hydrogen carbonate ion
HSO4-	Hydrogen sulfate ion
Additional info: See textbook Table 6.3 for more examples.

Writing Chemical Formulas

Formulas for Ionic Compounds

An ionic compound consists of positive and negative ions. The formula unit is the simplest representative particle and must be electrically neutral. The total positive charge equals the total negative charge.

• Example: Na+ + Cl- → NaCl

• Example: Ca2+ + 2Cl- → CaCl2

• Example: Al3+ + 3Cl- → AlCl3

• Example: Pb4+ + 2O2- → PbO2

For compounds with polyatomic ions:

• Example: 2K+ + SO42- → K2SO4

• Example: 2NH4+ + SO42- → (NH4)2SO4

Binary Ionic Compounds

Writing and Predicting Formulas

Binary ionic compounds are composed of a metal (cation) and a nonmetal (anion). The overall charge of the compound is zero. The cation is always written first, followed by the anion.

• Example: MgO (magnesium oxide)

• Example: Fe2O3 (iron(III) oxide)

• Example: CoN (cobalt(III) nitride)

Formulas for alkali metal chlorides (e.g., NaCl, LiCl, KCl) and alkaline earth metal chlorides (e.g., BaCl2, MgCl2, CaCl2, SrCl2) follow predictable patterns.

Ternary Ionic Compounds

Composition and Naming

Ternary ionic compounds contain a metal and two other elements, typically a monoatomic metal cation and a polyatomic oxyanion. The names usually end in -ate or -ite.

• Example: NaNO3 (sodium nitrate)

• Example: KClO3 (potassium chlorate)

• Example: KClO2 (potassium chlorite)

For transition metals, the charge must be determined before naming.

Binary Molecular Compounds

Composition and Naming

Binary molecular compounds are composed of two nonmetals. The order for writing elements is prescribed by IUPAC: C, P, N, H, S, I, Br, Cl, O, F. The simplest representative particle is a molecule.

• Examples: CH4, PH3, NH3, H2S, HI, HBr, HCl, H2O, HF

Naming rules:

• First element is named first.

• Second element gets the suffix -ide.

• Number of atoms indicated by Greek prefixes:

Number	Prefix
1	mono-
2	di-
3	tri-
4	tetra-
5	penta-
6	hexa-
7	hepta-
8	octa-
9	nona-
10	deca-

If two vowels occur together, the first is dropped (e.g., monoxide, tetroxide).

Binary Acids

Composition and Naming

Binary acids are aqueous solutions of compounds containing hydrogen and a nonmetal. They are produced by dissolving a binary molecular compound in water.

• Use the prefix hydro- before the nonmetal stem.

• Add the suffix -ic acid.

• Example: HCl(aq) → Hydrochloric acid

• Example: H2S(aq) → Hydrosulfuric acid

Ternary Oxyacids

Composition and Naming

Ternary oxyacids are aqueous solutions containing hydrogen and an oxyanion. The naming method attaches the suffix -ic acid to the nonmetal stem of the oxyanion.

• Example: HNO3(aq) → Nitric acid (from nitrate ion, NO3-)

• Example: HNO2(aq) → Nitrous acid (from nitrite ion, NO2-)

• Example: H2SO4(aq) → Sulfuric acid (from sulfate ion, SO42-)

• Example: H2SO3(aq) → Sulfurous acid (from sulfite ion, SO32-)

Summary Table: Types of Inorganic Compounds

Type	Composition	Example
Binary Ionic	Metal + Nonmetal	KCl, AlCl3
Ternary Ionic	Metal + Polyatomic Ion	KNO3, NaNO3
Binary Molecular	Two Nonmetals	H2O, NH3
Binary Acid	Hydrogen + Nonmetal (aq)	HCl(aq), H2S(aq)
Ternary Oxyacid	Hydrogen + Oxyanion (aq)	HNO3(aq), H2SO4(aq)

Key Equations and Concepts

• Charge Balance in Ionic Compounds:

• $\text{Total positive charge} = \text{Total negative charge}$

• General formula for ionic compounds:

• $\text{Cation}^{x+} + \text{Anion}^{y-} \rightarrow \text{Compound}$

• Example:

• $\text{Ca}^{2+} + 2\text{Cl}^{-} \rightarrow \text{CaCl}_2$

Additional info: For more detailed lists of ions and naming conventions, refer to textbook tables 6.1, 6.2, and 6.3. Exercises referenced in the notes provide practice for classification and naming.