Language of Chemistry: Classification and Naming of Inorganic Compounds

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Language of Chemistry

Classification of Inorganic Compounds

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

Binary Ionic Compounds: Composed of 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. 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).

Classifying Ions

Ions are atoms or groups of atoms with a net electrical charge. They are classified as follows:

Cation: A positively charged ion (e.g., Na+, Mg2+).
Anion: A negatively charged ion (e.g., Cl-, SO42-).
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-).

Monoatomic Ions

Naming Monoatomic Ions

The names of monoatomic cations are derived from the parent metal. If a metal can form more than one type of ion (common for transition metals), the charge is specified:

Stock System: Uses Roman numerals in parentheses to indicate charge. Example: Cu2+ is copper(II) ion.
Latin System: Uses suffixes -ous (lower charge) and -ic (higher charge). Example: Cu2+ is cupric ion.

Monoatomic anions are named by adding the suffix -ide to the stem of the nonmetal name.

Example: Cl- is chloride ion; O2- is oxide ion.

Common Monoatomic Ions

Cation	Name
Na+	Sodium ion
Mg2+	Magnesium ion
Fe2+	Iron(II) ion / ferrous ion
Fe3+	Iron(III) ion / ferric ion
Anion	Name
Cl-	Chloride ion
O2-	Oxide ion
S2-	Sulfide ion

Polyatomic Ions

Naming Polyatomic Ions

Polyatomic ions often 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
OH-: Hydroxide ion
NH4+: Ammonium ion

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

Writing Chemical Formulas

Formulas for Ionic Compounds

An ionic compound consists of positive and negative ions arranged so that the total charge is zero. The simplest unit is called a formula unit.

Rule: The sum of positive and negative charges must equal zero.
Example:
- Na+ + Cl- → NaCl
- Ca2+ + 2Cl- → CaCl2
- Al3+ + 3Cl- → AlCl3
- Pb4+ + 2O2- → PbO2

Formulas with Polyatomic Ions

2K+ + SO42- → K2SO4
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 formula is written with the cation first, followed by the anion. The overall charge must be zero.

Example: MgO is magnesium oxide.
Pattern: Alkali metal chlorides (LiCl, KCl, NaCl) and alkaline earth metal chlorides (MgCl2, CaCl2, BaCl2, SrCl2) follow predictable formulas.

Ternary Ionic Compounds

Definition and Naming

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

Example: NaNO3 is sodium nitrate.
Example: KClO3 is potassium chlorate; KClO2 is potassium chlorite.
If the metal is a transition metal, determine its charge before naming.

Binary Molecular Compounds

Definition and Naming

Binary molecular compounds consist of two nonmetals. The order of elements is prescribed by IUPAC: C, P, N, H, S, I, Br, Cl, O, F. The number of atoms is 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-

Naming: First element is named first; second element gets the suffix -ide.
Example: CO2 is carbon dioxide; N2O4 is dinitrogen tetroxide.
If two vowels meet, drop the first vowel (e.g., monoxide, tetroxide).

Binary Acids

Definition and Naming

Binary acids are aqueous solutions of compounds containing hydrogen and a nonmetal. The name is formed by:

Using the prefix hydro- before the nonmetal stem.
Adding the suffix -ic acid.
Example: HCl(aq) is hydrochloric acid; H2S(aq) is hydrosulfuric acid.

Ternary Oxyacids

Definition and Naming

Ternary oxyacids are aqueous solutions containing hydrogen and a polyatomic oxyanion. The name is formed by attaching -ic acid or -ous acid to the nonmetal stem of the oxyanion.

Example: HNO3(aq) is nitric acid (from nitrate ion).
Example: HNO2(aq) is nitrous acid (from nitrite ion).
Example: H2SO4(aq) is sulfuric acid (from sulfate ion); H2SO3(aq) is sulfurous acid (from sulfite ion).

Summary Table: Classification 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 + Nonmetal + Oxygen (aq)	HNO3(aq), H2SO4(aq)

Key Formulas

Additional info:

Greek prefixes are used only for molecular (covalent) compounds, not for ionic compounds.
Transition metals often require Roman numerals to indicate their charge in compound names.
Polyatomic ions are commonly found in both ionic compounds and acids.