IUPAC nomenclature of inorganic chemistry

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The IUPAC nomenclature of inorganic chemistry is a systematic method of naming inorganic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). Ideally, every inorganic compound should have a name from which an unambiguous formula can be determined. There is also an IUPAC nomenclature of organic chemistry.

The names "caffeine" and "3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione" both describe the same chemical. The systematic name encodes the structure and composition of the caffeine molecule in some detail, and provides an unambiguous reference to this compound, whereas the name "caffeine" just names it. These advantages make the systematic name far superior to the common name when absolute clarity and precision are required. However, even professional chemists will use the non-systematic name almost all of the time, because caffeine is a well-known common chemical with a unique structure. Similarly, H₂O is most often simply called water in English, though other chemical names do exist.

1. Single atom anions are named with an -ide suffix: for example, H⁻ is hydride.
2. Compounds with a positive ion (cation), the name of the compound is simply the cation's name (usually the same as the element's), followed by the anion. For example, NaCl is sodium chloride, and CaF₂ is calcium fluoride.
3. Cations able to take on more than one positive charge are labeled with Roman numerals in parentheses. For example, Cu⁺ is copper(I), Cu²⁺ is copper(II). An older, deprecated notation is to append -ous or -ic to the root of the Latin name to name ions with a lesser or greater charge. Under this naming convention, Cu⁺ is cuprous and Cu²⁺ is cupric. For naming metal complexes see the page on complex (chemistry).
4. Oxyanions (polyatomic anions containing oxygen) are named with -ite or -ate, for a lesser or greater quantity of oxygen. For example, NO₂⁻ is nitrite, while NO₃⁻ is nitrate. If four oxyanions are possible, the prefixes hypo- and per- are used: hypochlorite is ClO⁻, perchlorate is ClO₄⁻,
5. The prefix bi- is a deprecated way of indicating the presence of a single hydrogen ion, as in "sodium bicarbonate" (NaHCO₃). The modern method specifically names the hydrogen atom. Thus, NaHCO₃ would be pronounced "sodium hydrogen carbonate".

Positively charged ions are called cations and negatively charged ions are called anions. The cation is always named first. Ions can be metals or polyatomic ions. Therefore the name of the metal or positive polyatomic ion is followed by the name of the non-metal or negative polyatomic ion. The positive ion retains its element name whereas for a single non-metal anion the ending is changed to -ide.

Example: sodium chloride, potassium oxide, or calcium carbonate.

When the metal has more than one possible ionic charge or oxidation number the name becomes ambiguous. In these cases the oxidation number of the metal ion is represented by a Roman numeral in parentheses immediately following the metal ion name. For example in uranium(VI) fluoride the oxidation number of uranium is 6. Another example is the iron oxides. FeO is iron(II) oxide and Fe₂O₃ is iron(III) oxide.

An older system used prefixes and suffixes to indicate the oxidation number, according to the following scheme:

Thus the four oxyacids of chlorine are called hypochlorous acid (HOCl), chlorous acid (HOClO), chloric acid (HOClO₂) and perchloric acid (HOClO₃), and their respective conjugate bases are the hypochlorite, chlorite, chlorate and perchlorate ions. This system has partially fallen out of use, but survives in the common names of many chemical compounds: the modern literature contains few references to "ferric chloride" (instead calling it "iron(III) chloride"), but names like "potassium permanganate" (instead of "potassium manganate(VII)") and "sulfuric acid" abound.

Traditional naming

Naming simple ionic compounds

An ionic compound is named by its cation followed by its anion. See polyatomic ions for a list of possible ions.

For cations that take on multiple charges, the charge is written using Roman numerals in parentheses immediately following the element name) For example, Cu(NO₃)₂ is copper(II) nitrate, because the charge of two nitrate ions (NO₃^-1) is 2 × −1 = −2, and since the net charge of the ionic compound must be zero, the Cu ion has a 2+ charge. This compound is therefore copper(II) nitrate. In the case of cations with a 4+ oxidation state, the acceptable format for the Roman numeral 4 is IV and not IIII.

The Roman numerals in fact show the oxidation number, but in simple ionic compounds (i.e., not metal complexes) this will always equal the ionic charge on the metal. For a simple overview see [1], for more details see selected pages from IUPAC rules for naming inorganic compounds.

List of common ion names

Monatomic anions:

Cl⁻ chloride

S²⁻ sulfide

P³⁻ phosphide

Polyatomic ions:

NH₄⁺ ammonium

H₃O⁺ hydr-oxonium

NO₃⁻ nitrate

NO₂⁻ nitrite

ClO⁻ hypochlorite

ClO₂⁻ chlorite

ClO₃⁻ chlorate

ClO₄⁻ perchlorate

SO₃²⁻ sulfite

SO₄²⁻ sulfate

HSO₃⁻ hydrogen sulfite (or bisulfite)

HCO₃⁻ hydrogen carbonate (or bicarbonate)

CO₃²⁻ carbonate

PO₄³⁻ phosphate

HPO₄²⁻ hydrogen phosphate

H₂PO₄⁻ dihydrogen phosphate

CrO₄²⁻ chromate

Cr₂O₇²⁻ dichromate

BO₃³⁻ orthoborate

AsO₄³⁻ arsenate

C₂O₄²⁻ oxalate

CN⁻ cyanide

SCN⁻ thiocyanate

MnO₄⁻ permanganate

Naming hydrates

Hydrates are ionic compounds that have absorbed water. They are named as the ionic compound followed by a numerical prefix and -hydrate. The numerical prefixes used are listed below:

1. mono-
2. di-
3. tri-
4. tetra-
5. penta-
6. hexa-
7. hepta-
8. octa-
9. nona-
10. deca-

For example, CuSO₄ · 5H₂O is "copper(II) sulfate pentahydrate".

Naming molecular compounds

Inorganic molecular compounds are named with a prefix (see list above) before each element. The more electronegative element is written last and with an -ide suffix. For example, CO₂ is carbon dioxide. Although CCl₄ is sometimes called carbon tetrachloride under this rule, it is not an inorganic molecule and is more properly called tetrachloromethane. There are some exceptions to the rule, however. The prefix mono- is not used with the first element; for example, CO₂ is carbon dioxide, not "monocarbon dioxide". Sometimes prefixes are shortened when the ending vowel of the prefix "conflicts" with a starting vowel in the compound. This makes the compound easier to speak; for example, CO is "carbon monoxide" (as opposed to "monooxide").

Naming acids

Acids are named by the anion they form when dissolved in water. If an acid forms an anion named ___ide, it is named hydro___ic acid. For example, hydrochloric acid forms a chloride anion. With sulfur, however, the whole word is kept instead of the root: i.e.: hydrosulfuric acid. Secondly, anions with an -ate suffix are formed when acids with an -ic suffix are dissolved, e.g. chloric acid (HClO₃) dissociates into chlorate anions to form salts such as sodium chlorate (NaClO₃); anions with an -ite suffix are formed when acids with an -ous suffix are dissolved in water, e.g. chlorous acid (HClO₂) disassociates into chlorite anions to form salts such as sodium chlorite (NaClO₂).

2005 revision of IUPAC's nomenclature for inorganic compounds

See main article IUPAC nomenclature of inorganic chemistry 2005

See also

• IUPAC nomenclature
• IUPAC nomenclature of organic chemistry
• List of inorganic compounds
• Water of Crystallization

References

1. ^  Nomenclature of Inorganic Chemistry, Recommendations 1990, Oxford:Blackwell Scientific Publications. (1990)

External links

• IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) (online draft of an updated version of the "Red Book")
• Bibliography of IUPAC Recommendations on Inorganic Nomenclature (last updated 2004-02-17)
• ChemTeam Highschool Tutorial
• PDF file SUNY Potsdam.edu
• Nomenclature Tutorial