Nomenclature is a term that applies to either a list of names and/or terms, or to the system of principles, procedures and terms related to naming. The principles of naming vary from the relatively informal conventions of everyday speech to the internationally-agreed principles, rules and recommendations that govern the formation and use of the specialist terms used in scientific and other disciplines.
The most commonly cited authority for nomenclature conventions in chemistry is the IUPAC
"I learned very early the difference between knowing the name of something and knowing something"
- Richard Feynman (May 11, 1918 – February 15, 1988) American physicist known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics and the physics of the superfluidity of supercooled liquid helium, as well as in particle physics.
The name of an acid depends on the anion being protonated.
To name acids composed of H+ and a monoatomic anion, assign the prefix "hydro" and the suffix "ic" to the root word describing the anion.
Note that the only thing that changes between the names is the root word that describes the anion.
Many common acids are aqueous solutions of compounds containing one or more H+ cations ionically bonded an oxyanion. Memorizing the names of oxyanions is crucial to understanding acid nomenclature, as is understanding the difference between -ite and -ate in Oxyanion names. Oxyanions ending in ate contain one more oxygen atom than oxyanions ending in ite. It is important to note that oxyanions ending in ate do not always have a particular number of oxygen atoms: a sulfate anion (SO42-) for example, contains 4 oxygen atoms, while a chlorate anion (ClO3-) only contains 3. Because of this difference, it is helpful to memorize the ate in common oxyanion families, as all other names in the family can be easily derived from the knowledge of one.
A useful mnemonic for naming acids based on their anions is "ate-ic ite-ous". It is easily remembered, as it sounds like a disease caused by eating "icky" things, as in "I ate some ick, now I have 'ate-ic ite-ous'". It reminds a student that anions that end in -ate form acids ending in "-ic," and anions that end in -ite form acids ending in "-ous". SO32- and SO42- are called sulfite and sulfate, respectively, so an acid composed of hydrogen cations and sulfite would be H2SO3, "Sulfurous acid". The acid composed of hydrogen cations and sulfate is H2SO4, "Sulfuric acid". Note that in this series, like many, charge is independent of the number of oxygen atoms in a given oxyanion.
Oxyanions containing halogens form larger families of oxyanions, but the "ate-ic ite-ous" mnemonic still applies. The difference is that prefixes in oxyanion names, as listed below, are added to the acid name as well.
|Cl- chloride||HCl hydrochloric acid|
|ClO- hypochlorite||HClO hypochlorous acid|
|ClO2- chlorite||HClO2 chlorous acid|
|ClO3- chlorate||HClO3 chloric acid|
|ClO4- perchlorate||HClO4 perchloric acid|
Stock Nomenclature denotes the use of roman numerals after the name of a component element in a chemical compound. The numeral is necessary because many of the elements, namely the transition metals are stable in several different oxidation states.
Fe2O3, for example, is Iron(III) oxide. The roman numeral "III" is added to indicate that in this compound, Iron has an oxidation number of +3, or more simply, has a 3+ charge (Fe3+). This can be deduced from the chemical formula Fe2O3 by examining the charge of the anion present, and the amount of each ion present in the compound. An Oxide (O2-) anion always carries a 2- charge. Three oxide anions in each molecule of Fe2O3 means the total charge of the anions in one molecule is 6-. Since there are two Iron cations, each much posses a charge of 3+ to form a neutral molecule with the oxide anions.
Note that in the previous example, referring to Fe2O3 as "Iron(III) trioxide" is not necessary; one only needs to add a prefix when naming covalent compounds.