General Chemistry Nomenclature: Study Guide for Naming Compounds

Compound Nomenclature in General Chemistry

Introduction to Chemical Nomenclature

Chemical nomenclature is the systematic method of naming chemical compounds. Understanding how to name compounds is essential for clear communication in chemistry. Compounds are named according to the types of elements they contain and the rules set by IUPAC and other conventions.

Covalent (Molecular) Compounds

Identifying Covalent Compounds

Covalent compounds are formed between nonmetal elements. These elements are typically found on the right side of the periodic table.

• Key Point: Covalent compounds consist of two or more nonmetals.

• Example: CO2 (carbon dioxide), NO2 (nitrogen dioxide)

Naming Covalent Compounds

The naming system for covalent compounds uses Greek prefixes to indicate the number of atoms of each element in the molecule. The first element keeps its name, and the second element ends with "-ide." The prefix "mono-" is not used for the first element.

• Prefixes:

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

• Example: N2O4 is dinitrogen tetroxide.

Additional info: Do not use "mono-" for the first element. For example, SF6 is "sulfur hexafluoride," not "monosulfur hexafluoride."

Ionic Compounds

Identifying Ionic Compounds

Ionic compounds are formed between metals and nonmetals. Metals are found on the left side of the periodic table, and nonmetals on the right.

• Key Point: Ionic compounds consist of cations (positive ions, usually metals) and anions (negative ions, usually nonmetals).

• Example: NaCl (sodium chloride), MgS (magnesium sulfide)

Naming Simple Ionic Compounds

To name ionic compounds with elemental ions:

• Name the cation (metal) first, then the anion (nonmetal) with its ending changed to "-ide."

• Do not indicate the number of ions in the name.

• Example: Ca3P2 is calcium phosphide.

Naming Ionic Compounds with Transition Metals

Transition metals can have variable charges. The charge is indicated by a Roman numeral in parentheses after the cation name.

• Key Point: The charge of the transition metal is determined so that the total charge of the compound is zero.

• Example: Fe2O3: $2(x) + 3(-2) = 0$; $2x - 6 = 0$; $x = 3$; so the name is iron(III) oxide.

• Transition metals with constant charge: Ag+, Zn2+, Cd2+

Naming Ionic Compounds with Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms covalently bonded, acting as a single charged unit.

• Key Point: Name the cation first, then the polyatomic anion.

• Example: Na3PO4 is sodium phosphate; NH4Br is ammonium bromide.

• Common polyatomic ions:

Ion	Formula	Charge
Ammonium	NH4+	+1
Nitrate	NO3-	-1
Sulfate	SO42-	-2
Phosphate	PO43-	-3

Acids

Identifying Acids

Acids are compounds that contain hydrogen as the cation. They are classified based on the presence or absence of oxygen in the anion.

• Key Point: All acids contain hydrogen; the anion determines the naming convention.

Naming Binary Acids (No Oxygen)

Binary acids consist of hydrogen and one other nonmetal.

• Use the prefix "hydro-" followed by the root of the nonmetal and the suffix "-ic acid."

• Example: HCl is hydrochloric acid; HBr is hydrobromic acid.

Naming Oxyacids (Contain Oxygen)

Oxyacids contain hydrogen, oxygen, and another element (usually a nonmetal). The name is based on the polyatomic ion present.

• If the polyatomic ion ends in "-ate," change the ending to "-ic acid."

• If the polyatomic ion ends in "-ite," change the ending to "-ous acid."

• Example: H2SO4 (sulfate) is sulfuric acid; H2SO3 (sulfite) is sulfurous acid.

• Example: HNO3 (nitrate) is nitric acid; HNO2 (nitrite) is nitrous acid.

Additional info: Some acids have unusual root names, such as sulfuric acid (not "sulfic acid") and phosphoric acid (not "phosphic acid").

Summary Table: Naming Systems

Compound Type	Elements Involved	Naming System	Example
Covalent (Molecular)	Nonmetals	Greek prefixes, "-ide" ending	CO2: carbon dioxide
Ionic (Simple)	Metal + Nonmetal	Cation name + anion "-ide"	NaCl: sodium chloride
Ionic (Transition Metal)	Transition metal + Nonmetal	Cation name (Roman numeral) + anion "-ide"	FeCl3: iron(III) chloride
Ionic (Polyatomic)	Metal + Polyatomic ion	Cation name + polyatomic ion name	NaNO3: sodium nitrate
Acid (Binary)	Hydrogen + Nonmetal	"hydro-" + root + "-ic acid"	HCl: hydrochloric acid
Acid (Oxyacid)	Hydrogen + Polyatomic ion	"-ate" to "-ic acid", "-ite" to "-ous acid"	H2SO4: sulfuric acid

Practice and Application

• Practice naming compounds by identifying the type (covalent, ionic, acid) and applying the correct rules.

• Check for transition metals and polyatomic ions, as these affect the naming convention.

• Review the periodic table to identify metals, nonmetals, and transition metals.

Key Equations and Concepts

• Charge Balance in Ionic Compounds:

• $\text{Total positive charge} + \text{Total negative charge} = 0$

• Determining Transition Metal Charge:

• $\text{(Number of cations)} \times \text{(cation charge)} + \text{(Number of anions)} \times \text{(anion charge)} = 0$

Additional info: Mastery of nomenclature is essential for success in General Chemistry, as it forms the basis for understanding chemical formulas, reactions, and laboratory work.