Chapter 6: Language of Chemistry – Classification and Naming of Inorganic Compounds

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Language of Chemistry

Introduction to Chemical Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) sets the global standards for naming chemical compounds. Understanding these rules is essential for clear communication in chemistry, especially when classifying and naming inorganic compounds.

Classification of Inorganic Compounds

Main Classes of Inorganic Compounds

Most inorganic compounds do not contain carbon, with exceptions such as carbon dioxide (CO2) and carbonates (CO32–). Inorganic compounds are classified into five common types:

Binary ionic compounds
Ternary ionic compounds
Binary molecular compounds
Binary acids
Ternary oxyacids

Classification of inorganic compounds and acids

Ionic Compounds

Ionic compounds are formed from the combination of metals and nonmetals. They are classified as:

Binary ionic compounds: Contain two elements (one metal, one nonmetal). Examples: NaCl, AlCl3.
Ternary ionic compounds: Contain three elements, often including oxygen. Examples: KNO3, Al(NO3)3.

Molecular Compounds

Binary molecular compounds consist of two nonmetal elements. Examples include ammonia (NH3) and water (H2O).

Molecular structure of P4S3

Aqueous Acids

Acids are classified based on their composition:

Binary acids: Aqueous solutions containing hydrogen and a nonmetal (e.g., HCl(aq)).
Ternary oxyacids: Aqueous solutions containing hydrogen, oxygen, and another nonmetal (e.g., HNO3(aq)).

Structure of HF acid

Classification of Ions

Types of Ions

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

Cations: Positively charged ions (e.g., Na+, Mg2+).
Anions: Negatively charged ions (e.g., Cl–, SO42–).
Polyatomic ions: Groups of atoms with a charge (e.g., NO3–).

Classification of ions

Monoatomic Ions

Monoatomic ions are single atoms with a charge. Metals lose electrons to form cations, named after the element (e.g., sodium ion, magnesium ion). Nonmetals gain electrons to form anions, named by adding the suffix -ide to the root name (e.g., chloride, oxide).

Table of common monoatomic anions

Charge Determination for Monoatomic Ions

Metal cations (A groups): Charge equals the family number on the periodic table.
Nonmetal anions (A groups): Charge equals the family number minus eight.
Exceptions: Tin and lead (Group IVA/14) form both 2+ and 4+ ions; many transition metals can have multiple charges.

Periodic table with common ion charges

Polyatomic Ions

Polyatomic ions are composed of multiple atoms, often including oxygen. Oxyanions are named with the suffix -ate or -ite:

-ate: Indicates more oxygen atoms (e.g., nitrate NO3–).
-ite: Indicates fewer oxygen atoms (e.g., nitrite NO2–).
-ide: Used for hydroxide (OH–) and cyanide (CN–).

Table of common polyatomic ions

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., KBr, CaO).
If charges are not equal: use subscripts to balance charges (e.g., BaCl2, Li2S).
For polyatomic ions: use parentheses if more than one is needed (e.g., (NH4)2SO4).

Determining Ion Charges in Compounds

For metals with multiple possible charges, determine the charge based on the anion. Example: In Cr3N2, each Cr is 2+ because the total negative charge from N3– is 6–.

Naming Chemical Compounds

Naming Binary Ionic Compounds

Combine the cation and anion names (drop the word "ion"), with the cation first and the anion second. Add the suffix -ide to the anion.

Example: MgO is magnesium oxide.
Example: HgS is mercury(II) sulfide.

Structure of HgS (cinnabar)

Predicting Formulas from Names

To determine the formula from the name, use the charges of the ions and balance them so the total charge is zero. Example: Iron(III) fluoride is FeF3 because Fe3+ and F– combine in a 1:3 ratio.

Naming Ternary Ionic Compounds

Name the cation followed by the anion. If the metal can have more than one oxidation state, indicate the charge with Roman numerals.

Example: KClO2 is potassium chlorite.
Example: Co(ClO3)3 is cobalt(III) chlorate.

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.

Table of Greek prefixes for binary molecular compounds

Example: P4S3 is tetraphosphorus trisulfide.
Exception: If there is only one atom of the first element, "mono-" is not used (e.g., CO is carbon monoxide).

Naming Acids

Binary Acids

Binary acids are aqueous solutions containing hydrogen and a nonmetal. The formula begins with H. Name by using the prefix hydro- and the suffix -ic acid.

Example: HF(aq) is hydrofluoric acid.
Example: HI(aq) is hydroiodic acid.

Structure of HF acid

Ternary Oxyacids

Ternary oxyacids are aqueous solutions containing hydrogen and an oxyanion. If the acid is derived from an oxyanion ending in -ate, change the suffix to -ic acid. If derived from -ite, change the suffix to -ous acid.

Example: HNO3(aq) is nitric acid (from nitrate).
Example: HNO2(aq) is nitrous acid (from nitrite).

Table of ternary oxyacids and related compounds

Summary Tables

Common Monoatomic Anions

Anion	IUPAC Name	Anion	IUPAC Name
Br–	bromide ion	N3–	nitride ion
Cl–	chloride ion	O2–	oxide ion
F–	fluoride ion	P3–	phosphide ion
I–	iodide ion	S2–	sulfide ion

Common Polyatomic Ions

Cation	IUPAC Name	Anion	IUPAC Name
NH4+	ammonium ion	CH3COO–	acetate ion
		CO32–	carbonate ion
		ClO–	hypochlorite ion
		ClO2–	chlorite ion
		ClO3–	chlorate ion
		ClO4–	perchlorate ion
		CN–	cyanide ion
		HCO3–	hydrogen carbonate ion
		HSO4–	hydrogen sulfate ion
		OH–	hydroxide ion
		NO2–	nitrite ion
		NO3–	nitrate ion
		SO42–	sulfate ion
		SO32–	sulfite ion

Greek Prefixes for Binary Molecular Compounds

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

Ternary Oxyacids and Related Compounds

Ternary	Oxyacid	Ternary	Compound
HClO	hypochlorous acid	NaClO	sodium hypochlorite
HClO2	chlorous acid	NaClO2	sodium chlorite
HClO3	chloric acid	NaClO3	sodium chlorate
HClO4	perchloric acid	NaClO4	sodium perchlorate

Summary

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"; charge indicated with Roman numerals if multiple possible charges.
Ionic compounds: cation first, anion second, anion ends with "-ide".
Molecular compounds: elements in order C, P, N, H, S, I, Br, Cl, O, F; Greek prefixes indicate atom count.
Acids: binary acids use "hydro-" and "-ic acid"; ternary oxyacids use "-ic acid" or "-ous acid" based on oxyanion suffix.