1.3 Nomenclature

Overview of Chemical Naming

  • IUPAC (International Union of Pure and Applied Chemistry): Establishes universal naming rules for consistency and clear communication among chemists globally.

  • Compound Classification: Compounds are categorized to determine the correct naming conventions:

    • Covalent: Binary molecular compounds, Hydrocarbons, Acids.

    • Ionic: Ammonium-containing, Monovalent metal cations, Divalent/multivalent metal cations.

    • Bases: Typically named similar to ionic compounds, containing a metal cation and a hydroxide ion.

  • Initial Naming Step: The first crucial step is to determine if a compound is ionic (formed between a metal and a nonmetal, or containing polyatomic ions) or covalent (formed between two nonmetals). This distinction guides the entire naming process.

Naming Covalent Compounds

  • Binary Molecular Compounds (Two Elements): These compounds are composed of two different nonmetal elements.

    • Use numerical prefixes (mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, etc.) to indicate the number of atoms of each element.

    • The first element is named with its full element name. The prefix mono- is generally omitted for the first element if there is only one atom.

    • The second element is named by taking its base name and adding the "-ide" ending. The order of elements in the name often follows the less electronegative element first.

    • Example: P2O5 is Diphosphorus pentoxide (two phosphorus, five oxygen atoms); CO2 is Carbon dioxide; SF6 is Sulfur hexafluoride.

  • Hydrocarbons (Only H and C): Organic compounds that contain only hydrogen and carbon atoms.

    • The prefix for the carbon chain is based on the number of carbon atoms:

    • 1 = meth-

    • 2 = eth-

    • 3 = prop-

    • 4 = but-

    • 5 = pent-

    • 6 = hex-

    • 7 = hept-

    • 8 = oct-

    • The suffix indicates the type of carbon-carbon bond present:

    • Alkanes (Single bonds): End with "-ane", indicating all single C-C bonds. General formula CnH{2n+2}. E.g., C5H{12} is Pentane.

    • Alkenes (Double bonds): End with "-ene", indicating at least one C=C double bond. General formula CnH{2n}. E.g., C5H{10} is Pentene.

    • Alkynes (Triple bonds): End with "-yne", indicating at least one C[TripleBond]C triple bond. General formula CnH{2n-2}. E.g., C5H8 is Pentyne.

Naming Acids

  • Binary Acids (Two Elements): These acids always contain hydrogen and one other nonmetal, typically from Group 16 or 17.

    • Use the prefix "hydro-".

    • Combine the root name of the nonmetal anion with the ending "-ic acid".

    • Example: HF is Hydrofluoric acid; HCl is Hydrochloric acid.

  • Tertiary Acids (Oxyacids - Three or More Elements, with Polyatomic Ions): These acids generally contain hydrogen, oxygen, and another nonmetal atom. They are derived from polyatomic ions containing oxygen.

    • If the polyatomic anion's name ends in "-ate", the acid's name ends in "-ic acid". Example: Sulfate (SO4^{2-}) forms Sulfuric acid (H2SO4); Nitrate (NO3^-) forms Nitric acid (HNO_3).

    • If the polyatomic anion's name ends in "-ite", the acid's name ends in "-ous acid". Example: Phosphite (PO3^{3-}) forms Phosphorous acid (H3PO3); Nitrite (NO2^-) forms Nitrous acid (HNO_2).

    • No "hydro-" prefix is used for oxyacids.

Naming Ionic Compounds

  • Ionic compounds are formed between a metal and a nonmetal, or contain polyatomic ions. They consist of a positively charged cation and a negatively charged anion.

  • The cation (positive ion) is always named first, followed by the anion (negative ion).

  • Chemical formulas for ionic compounds are always written in the simplest empirical ratio, representing the lowest whole-number ratio of ions.

  • The overall compound charge must be neutral, meaning the total positive charge from the cations balances the total negative charge from the anions.

  • It's important to recognize common polyatomic ions (e.g., Ammonium NH4^+, Hydroxide OH^-, Sulfate SO4^{2-}, Phosphate PO_4^{3-}) for correct naming.

  • Ammonium Compounds: These are ionic compounds where the cation is always the ammonium ion (NH_4^+).

    • If the anion is a simple element, its name takes an "-ide" ending. E.g., Ammonium chloride (NH_4Cl).

    • If the anion is a polyatomic ion, its full polyatomic ion name is used. E.g., Ammonium sulfate ((NH4)2SO_4).

  • Monovalent Ionic Compounds (Cation with one possible charge): Metals that typically form only one stable cation charge (e.g., Group 1 alkali metals, Group 2 alkaline earth metals, Aluminum Al^{3+}, Zinc Zn^{2+}, Silver Ag^+).

    • Cation: Named using the full element name.

    • Anion (simple): Named by adding an "-ide" ending to its base name. E.g., Silver chloride (AgCl); Sodium bromide (NaBr).

    • Anion (polyatomic): The full polyatomic ion name is used. E.g., Magnesium nitrate (Mg(NO3)2); Calcium carbonate (CaCO_3).

  • Divalent Ionic Compounds (Cation with multiple possible charges - Stock System): Transition metals and some heavier main-group metals (e.g., lead, tin) can form ions with different charges.

    • Cation: Named using the full element name followed by a Roman numeral in parentheses, which specifies the exact charge of the metal cation within that particular compound.

    • Anion (simple): Named with an "-ide" ending. E.g., Iron(III) oxide (Fe2O3); Copper(I) chloride (CuCl).

    • Anion (polyatomic): The full polyatomic ion name is used. E.g., Copper(II) sulfate (CuSO_4).

    • The Roman numeral is crucial for specifying the metal's charge to ensure the compound's overall neutrality. For example, in Fe2O3, since each oxygen ion is O^{2-}, and there are three of them (3 \times 2- = 6- total negative charge), the two iron ions must account for a 6+ total positive charge; thus, each iron ion is 3+ (Iron(III)).

Naming Bases

  • Bases contain the hydroxide (OH^-) ion as their characteristic anion.

  • They are typically named like monovalent ionic compounds, with the metal cation's name followed by "hydroxide".

  • Example: NaOH is