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Systematic name

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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.

Table of contents

1 Chemical Names

1.1 Naming Ionic Compounds
1.2 Naming Hydrates
1.3 Naming Molecular Compounds
1.4 Naming Acids

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.

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

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.

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.

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.

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 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 sulfate pentahydrate because it has five water molecules.

Naming Molecular Compounds

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 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.