Inorganic Nomenclature

Categorization of Inorganic Compounds

Inorganic compounds are divided into two main categories: ionic and molecular. The classification of a particular compound dictates the specific rules required to name it correctly.

Nomenclature for Ionic Compounds

Ionic compounds consist of positively charged ions, known as cations, joined with negatively charged ions, known as anions. The naming convention requires writing the name of the cation first, which is then followed by the name of the anion.

Classification and Naming of Cations

Cations are organized into three distinct categories: monatomic cations with a constant oxidation state, monatomic cations with a varying oxidation state, and polyatomic cations.

Monatomic Cations with Constant Oxidation State

These ions maintain a fixed charge and are named by using the name of the element from which they are derived. For instance, $Na^+$ is referred to as the sodium ion.

• General Group Rules: Elements in groups IA, IIA, and IIIA typically form ions with charges corresponding to their group number ($+1$, $+2$, and $+3$ respectively).
• Specific Common Constant Ions:
  • $H^+$
  • $Ag^+$
  • $Zn^{2+}$
  • $Cd^{2+}$

Monatomic Cations with Varying Oxidation State

Monatomic cations that can exist in more than one oxidation state utilize two naming systems:

• Stock System: The name of the element is followed by the oxidation state indicated by a Roman numeral in parentheses.
• Classical System: The root name of the element is used with a specific suffix. The suffix $-ous$ denotes the lower oxidation state, while the suffix $-ic$ denotes the higher oxidation state.

Ions with $+1$ or $+2$ Oxidation States

• Copper:
  • $Cu^+$: Copper(I) ion or Cuprous ion
  • $Cu^{2+}$: Copper(II) ion or Cupric ion
• Mercury:
  • $Hg_2^{2+}$: Mercury(I) ion or Mercurous ion
  • $Hg^{2+}$: Mercury(II) ion or Mercuric ion

Ions with $+2$ or $+3$ Oxidation States

• Chromium:
  • $Cr^{2+}$: Chromium(II) ion or Chromous ion
  • $Cr^{3+}$: Chromium(III) ion or Chromic ion
• Manganese:
  • $Mn^{2+}$: Manganese(II) ion or Manganous ion
  • $Mn^{3+}$: Manganese(III) ion or Manganic ion
• Iron:
  • $Fe^{2+}$: Iron(II) ion or Ferrous ion
  • $Fe^{3+}$: Iron(III) ion or Ferric ion
• Cobalt:
  • $Co^{2+}$: Cobalt(II) ion or Cobaltous ion
  • $Co^{3+}$: Cobalt(III) ion or Cobaltic ion
• Nickel:
  • $Ni^{2+}$: Nickel(II) ion or Nickelous ion
  • $Ni^{3+}$: Nickel(III) ion or Nickelic ion

Ions with $+2$ or $+4$ Oxidation States

• Tin:
  • $Sn^{2+}$: Tin(II) ion or Stannous ion
  • $Sn^{4+}$: Tin(IV) ion or Stannic ion
• Lead:
  • $Pb^{2+}$: Lead(II) ion or Plumbous ion
  • $Pb^{4+}$: Lead(IV) ion or Plumbic ion

Ions with $+3$ or $+5$ Oxidation States

• Arsenic:
  • $As^{3+}$: Arsenic (III) ion
  • $As^{5+}$: Arsenic (V) ion
• Antimony:
  • $Sb^{3+}$: Antimony(III) ion
  • $Sb^{5+}$: Antimony(V) ion
• Bismuth:
  • $Bi^{3+}$: Bismuth (III) ion
  • $Bi^{5+}$: Bismuth(V) ion

Polyatomic Cations

Cations made of more than two elements bonded together that possess a net overall charge are polyatomic. The most common examples are:

• $NH_4^+$: Ammonium ion
• $H_3O^+$: Hydronium ion

Classification and Naming of Anions

Anions are generally categorized into two groups based on their suffixes and composition.

Anions with the $-ide$ Suffix

These are typically single-element (monatomic) anions that generally do not contain oxygen. Elements in groups VIIA, VIA, and VA form anions with $-1$, $-2$, and $-3$ charges by replacing the element's ending with $-ide$.

• Group VIIA ($-1$):
  • $F^-$: fluoride
  • $Cl^-$: chloride
  • $Br^-$: bromide
  • $I^-$: iodide
• Group VIA ($-2$):
  • $O^{2-}$: oxide
  • $S^{2-}$: sulfide
  • $Se^{2-}$: selenide
  • $Te^{2-}$: telluride
• Group VA ($-3$):
  • $N^{3-}$: nitride
  • $P^{3-}$: phosphide
  • $As^{3-}$: arsenide

Non-Monatomic $-ide$ Anions

• $OH^-$: hydroxide
• $CN^-$: cyanide
• $O_2^{2-}$: peroxide
• $N_3^-$: azide

Anions with $-ate$ or $-ite$ Suffixes

These contain at least two elements and typically include oxygen (or sulfur if oxygen is absent).

Commonly Cited Anions

• $OCN^-$: cyanate
• $SCN^-$: thiocyanate
• $SO_4^{2-}$: sulfate
• $S_2O_3^{2-}$: thiosulfate
• $HSO_4^-$: bisulfate or hydrogen sulfate
• $CO_3^{2-}$: carbonate
• $HCO_3^-$: bicarbonate or hydrogen carbonate
• $CrO_4^{2-}$: chromate
• $Cr_2O_7^{2-}$: dichromate
• $MnO_4^{2-}$: manganate
• $MnO_4^-$: permanganate
• $C_2H_3O_2^-$: acetate
• $BO_3^{3-}$: borate
• $AsO_4^{3-}$: arsenate
• $SiO_4^{4-}$: silicate

Recursive Naming Rules for Oxoanions

Specific "base" ions can be used to determine the names of related ions containing different amounts of oxygen:

• Base Form: $-ate$ (e.g., $ClO_3^-$ is chlorate; $IO_3^-$ is iodate; $BrO_3^-$ is bromate; $NO_3^-$ is nitrate; $PO_4^{3-}$ is phosphate).
• One more oxygen: $per-$ [root] $-ate$ (e.g., $ClO_4^-$ is perchlorate).
• One less oxygen: $-ite$ (e.g., $ClO_2^-$ is chlorite).
• Two less oxygens: $hypo-$ [root] $-ite$ (e.g., $ClO^-$ is hypochlorite).

Nomenclature for Acids

Acids are compounds that typically contain Hydrogen ($H$) as the cation. Naming depends on the suffix of the anion paired with the hydrogen.

Acids from $-ide$ Anions

Anions ending in $-ide$ form acids using the prefix $hydro-$ and the suffix $-ic$.

• Examples:
  • $HF$: Hydrofluoric acid
  • $HCl$: Hydrochloric acid
  • $HBr$: Hydrobromic acid
  • $HI$: Hydroiodic acid
  • $HCN$: Hydrocyanic acid
  • $H_2S$: Hydrosulfuric acid

Acids from $-ate$ or $-ite$ Anions

• $per-$ … $-ate$ anions form $per-$ … $-ic$ acids (e.g., $ClO_4^-$ perchlorate forms $HClO_4$ perchloric acid).
• $-ate$ anions form $-ic$ acids (e.g., $ClO_3^-$ chlorate forms $HClO_3$ chloric acid).
• $-ite$ anions form $-ous$ acids (e.g., $ClO_2^-$ chlorite forms $HClO_2$ chlorous acid).
• $hypo-$ … $-ite$ anions form $hypo-$ … $-ous$ acids (e.g., $ClO^-$ hypochlorite forms $HClO$ hypochlorous acid).

Nomenclature for Molecular Compounds

Molecular compounds are typically binary compounds composed of non-metal elements. They are named using numerical prefixes.

Naming Steps

1. First Non-metal: Write the name of the first non-metal. If there is only one, no prefix is used. If there are more than one, use the corresponding prefix.
2. Second Non-metal: Write the name of the second non-metal with the $-ide$ suffix and always attach a numerical prefix.

Prefixes for Molecular Compounds

• $1$: mono (used for the second element only)
• $2$: di
• $3$: tri
• $4$: tetra
• $5$: penta
• $6$: hexa
• $7$: hepta
• $8$: octa
• $9$: nina
• $10$: deca

Example: $N_2O_5$ is named dinitrogen pentoxide.