Chemistry

Chemical Formulation: General Principles

Basic principles of IUPAC, Stock and traditional nomenclature. Calculation of oxidation numbers and ion dissociation.

We distinguish the main element in the formula as the one on the right, which will be a non-metal, and uses its negative valence. The rest of the elements use their positive valences.
  • IUPAC Nomenclature, also called Systematic, compositional, Multiplier Prefixes or Stoichiometric: Uses Greek numerical prefixes to indicate the number of atoms of each element in the formula.
  • Stock Nomenclature, or with Oxidation Numbers: The oxidation number of the secondary element is indicated in Roman numerals. If it only has one possible oxidation number, it is omitted. Ex.: SO3SO_3, sulfur(VI) oxide.
  • Charge Numbers: Similar to the previous nomenclature. It indicates the charge of the cation but in Arabic numerals with a sign. Only for ionic compounds. Metal with non-metal.
  • Traditional Nomenclature: The oxidation number used by the secondary element is distinguished by adding prefixes and suffixes to the element's name. Several cases are distinguished depending on whether it has 1, 2, 3 or 4 valences as indicated. Note the special case of Manganese which uses 3 valences in acidic compounds.
4 val{3 val{2 val{1 val→hypo … ous… ous… icper … icMn(+4,+6,+7)Examples {SOhyposulfurous anhydrideSO2sulfurous anhydrideSO3sulfuric anhydride\begin{matrix} 4\text{ val}\begin{cases} 3\text{ val}\begin{cases} 2\text{ val}\begin{cases} 1\text{ val} \to \text{hypo } \dots \text{ ous} \\ \dots \text{ ous} \end{cases}\\ \dots \text{ ic} \end{cases}\\ \text{per } \dots \text{ ic} \end{cases} & Mn(+4, +6, +7) & \text{Examples } \begin{cases} SO & \text{hyposulfurous anhydride} \\ SO_2 & \text{sulfurous anhydride} \\ SO_3 & \text{sulfuric anhydride} \end{cases} \end{matrix}
  • Addition Nomenclature: Gives information about the structure of the molecule, but requires knowing the bonds.
  • We start from the known oxidation numbers. The element on the right in the formula is the most electronegative. It uses its negative oxidation number. The rest use their positive ones.
  • The molecule has a neutral charge, so the algebraic sum must be 0. With this condition we calculate the unknown oxidation number.
S?O2−S?O2(2−)⋅2H1+Cl?O2−H2(1+)⋅2S?O4(2−)⋅4↓↓↓↓S2+O2−S4+O24−H1+Cl1+O2−H2(1+)⋅2S6+O4(2−)⋅4\begin{matrix} \overset{?}{S}\overset{2-}{O} & \overset{?}{S}\overset{(2-)\cdot 2}{O_2} & \overset{1+}{H}\overset{?}{Cl}\overset{2-}{O} & \overset{(1+)\cdot 2}{H_2}\overset{?}{S}\overset{(2-)\cdot 4}{O_4} \\ \downarrow & \downarrow & \downarrow & \downarrow \\ \overset{2+}{S}\overset{2-}{O} & \overset{4+}{S}\overset{4-}{O_2} & \overset{1+}{H}\overset{1+}{Cl}\overset{2-}{O} & \overset{(1+)\cdot 2}{H_2}\overset{6+}{S}\overset{(2-)\cdot 4}{O_4} \end{matrix}
  • We start from the oxidation numbers of each element in a compound.
  • The compound dissociates into its cation and anion.
  • The net charge is the algebraic sum of their oxidation numbers.
H21+S2−→2H1++S2−→2(H)1++(S)2−H21+S6+O42−→2H1++S6+O42−→2(H)1++(SO4)2−\begin{aligned} \overset{1+}{H_2} \overset{2-}{S} &\to 2\overset{1+}{H} + \overset{2-}{S} \to 2(H)^{1+} + (S)^{2-} \\ \overset{1+}{H_2} \overset{6+}{S} \overset{2-}{O_4} &\to 2\overset{1+}{H} + \overset{6+}{S}\overset{2-}{O_4} \to 2(H)^{1+} + (SO_4)^{2-} \end{aligned}