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: $P<em>2O</em>5$ is Diphosphorus pentoxide (two phosphorus, five oxygen atoms); $CO<em>2$ is Carbon dioxide; $SF</em>6$ 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 $C<em>nH</em>{2n+2}$. E.g., $C<em>5H</em>{12}$ is Pentane.

  • Alkenes (Double bonds): End with "-ene", indicating at least one C=C double bond. General formula $C<em>nH</em>{2n}$. E.g., $C<em>5H</em>{10}$ is Pentene.

  • Alkynes (Triple bonds): End with "-yne", indicating at least one C[TripleBond]C triple bond. General formula $C<em>nH</em>{2n-2}$. E.g., $C<em>5H</em>8$ 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 ($SO<em>4^{2-}$) forms Sulfuric acid ($H</em>2SO<em>4$); Nitrate ($NO</em>3^-$) forms Nitric acid ($HNO_3$).

  • If the polyatomic anion's name ends in "-ite", the acid's name ends in "-ous acid". Example: Phosphite ($PO<em>3^{3-}$) forms Phosphorous acid ($H</em>3PO<em>3$); Nitrite ($NO</em>2^-$) 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 $NH<em>4^+$, Hydroxide $OH^-$, Sulfate $SO</em>4^{2-}$, 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 ($(NH<em>4)</em>2SO_4$).

• 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 ($Mg(NO<em>3)</em>2$); 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 ($Fe<em>2O</em>3$); 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 $Fe<em>2O</em>3$, 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