Systematic name





There are millions of possible objects that can be described in science, too
many to create common names for every one. As a response, a number of
systems of systematic names have been created.

These can be as simple as assigning a prefix and a number to each object (in
which case they are a sort of catalog reference), or as complex as encoding
the complete structure of the object in the name. Many systems combine some
information about the named object with an extra sequence number to make it
into a unique identifier.

   * Systematic names for chemical elements and chemical compounds
     (administered by IUPAC)
   * Systematic names for asteroids, comets, stars and other astronomical
     objects (administered by the International Astronomical Union)
   * Systematic names for genes, proteins, and other objects of molecular
     biology

Systematic names often co-exist with earlier common names assigned before
the creation of any systematic naming system. For example, many common
chemicals are still referred to by their common names, even by chemists.

Chemical Names

To give an example of why this is so, consider this example. 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 caffiene 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 is required. However, even
professional chemists will use the non-systematic name 99% of the time,
because caffeine is a well-known common chemical with a unique structure.

  1. Single atom anions are named with an -ide prefix, for example H+ is hydride.

  1. Compounds with a positive ion (cation), the name of the compound is
     simply the element name, with an -ide ending. For example, NaCl is
     sodium chloride, and CaF2 is calcium fluoride.

  1. Cations able to take on more than one positive charge are labeled with
     Roman numerals in parenthesises. For example, Cu+ is copper (I), Cu2+
     is copper (II). An older 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.

  1. 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.

  1. The prefix bi- is used to indicate the presense of a single hydrogen ion.

Naming 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 in Roman numerals - for example,
Cu(NO3)2 is copper(II) nitrate, because the charge of two nitrate ions 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.

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 prefixes
used are listed below:

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

For example, CuSO4*5H2O is copper sulfate pentahydrate because it has five
water molecules.

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, and CCl4 is carbon
tetrachloride. There are some exceptions to the rule, however. Sometimes
prefixes are shortened to make the name easier to say; for example, CO is
carbon monoxide (as opposed to monooxide).

Naming Organic Compounds

The naming sceme for organic compounds is complex and still developing, as
is knowledge of the compounds themselves. Where the parent structure is an
alkane, a comprehensive system of names exists.

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. Secondly, anions with an -ate
suffix are formed from acids with an -ic suffix are dissolved -- chloric
acid dissociates to chlorate anions in water. Thirdly, anions with an -ite
suffix are formed when acids with an -ous suffix are dissolved in water; for
example chlorous acid disassociates into chlorite anions.