A chemical nomenclature is a set of rules to generate systematic names for chemical compounds. IUPAC nomenclature is worldwide the most used chemical nomenclature. It is developed and kept up to date under the auspices of the International Union of Pure and Applied Chemistry (IUPAC). 

The primary function of chemical nomenclature is to ensure that a spoken or written chemical name leaves no ambiguity as to what chemical compound the name refers: each chemical name should refer to a single substance. A less important aim is to ensure that each substance has a single name, although the number of acceptable names is limited.

The IUPAC system is often criticized for the above failures when they become relevant (for example in differing reactivity of sulfur allotropes which IUPAC doesn't distinguish). While IUPAC has a human-readable advantage over CAS numbering, it would be difficult to claim that the IUPAC names for some larger, relevant molecules (such as rapamycin) are human-readable, and so most researchers simply use the informal names.and how they are formed.

Types of nomenclature

Organic chemistry
→Substitutive name
→Functional class name, also known as a radicofunctional name
→Conjunctive name
→Additive name
→Subtractive name
→Multiplicative name
→Fusion name
→Hantzsch–Widman name
→Replacement name

Inorganic chemistry
IUPAC nomenclature of inorganic chemistry

Compositional nomenclature
Examples of compositional names are:
PCl₅ phosphorus pentachloride
N₂O₄ dinitrogen tetraoxide
An alternative method uses the oxidation state on the metal in place of suffices, e.g.:
SnCl₂, tin(II) chloride as an alternative to tin dichloride.
Generally this system, known as Stock nomenclature or international nomenclature, is preferred over the prefix system for ionic compounds.

Substitutive nomenclature
This naming method generally follows established IUPAC organic nomenclature. Hydrides of the main group elements (groups 13–17) are given -ane base names, e.g. borane (BH₃), oxidane (H₂O), phosphane (PH₃) (the name phosphine is also in common use, but is not recommended by IUPAC). The compound PCl₃ would be named substitutively as trichlorophosphane.

Additive nomenclature
This naming method has been developed principally for coordination compounds although it can be more widely applied. An example of its application is:

[CoCl(NH₃)₅]Cl₂ pentaamminechloridocobalt(III) chloride
Note that ligands such as chloride become chlorido- rather than chloro- as in substitutive naming.