The terminology of chemical compounds is defined as Nomenclature
. Basically nomenclature represents the language of chemistry and help in understanding the different terms of chemical compounds used in chemistry.
- Nomenclature makes chemistry a bit easier and safer for everyone as by using naming of chemical compounds we can able to identify them and their uses in laboratory.
- Apart from chemistry, the scientific necessity for a simple system which is accepted internationally for naming objects of the natural world has been generated many formal nomenclature systems.
- For example, the best known nomenclature systems is the biological nomenclature which govern the Latinized scientific names of organisms.
- For the naming of chemical compounds in chemistry, the IUPAC nomenclature is international accepted system which maintained by the International Union of Pure and Applied Chemistry.
- The chemical nomenclature provides the methodology for assigning names and formula to the given chemical species so that they can be identify easily thereby facilitating communication.
- There must be some standardization in nomenclature so can be adopted by everyone. During the development of a system of nomenclature many factors are born in mined like public needs and common usage.
Sometimes the only requirement may be to identify a substance, thus the local names or common name and abbreviations are still used by and adopted by IUPAC system, as they are very popular and it’s not possible to replace them from terminology.
Generally local names do not convey structural and compositional information to a wider audience hence to a nomenclature system required which must be recognizable and unambiguous.
Nomenclature of chemical compounds is based on the type of elements involve in given chemical compounds. All known elements can be classified in two types.
- Metal and
Metals are electropositive elements and easily lose their valence electron to form cation. Hence they are good reducing agents and show positive oxidation states. In periodic table elements located from group-1 to 12 are metallic in nature. However from group-13 to 17 are non-metallic in nature. They have 5, 6 or 7 electrons in their valence shell and have tendency to accept electron to form anions. Hence non-metals are good oxidizing agent and show negative oxidation states.
These two types of elements can combine in three possible ways.
- Type I: These compounds composed of a metal cation which can show only one possible positive oxidation state and a non-metal anion. These chemical compounds are bonded by ionic bond and known as ionic compounds.
- Type II: They are also like type only, but here metal can show more than one possible positive oxidation state.
- Type III: These chemical compounds composed of only non-metals and bonded with covalent bond, thus called as covalent compounds.
In general any inorganic compound can be consisting of one cation and one anionic part. There are certain rule for nomenclature of cation and anionic part of inorganic compounds.
1. Nomenclature of Cation Basics
For the nomenclature of cation part of all the three types, there are different rules.Type I:
As these metal shows only one oxidation state, use name of element or name of element with term ‘ion’.
Na + = sodium ionType II:
Mg +2 = magnesium ion
NH4 + = ammonium ion
H3O+ = hydronium ion
These metal ions can show more than one oxidation states, the oxidation state or charge is written in roman numerals in parentheses just after name of metal and followed by ion.
Cu +2 = copper (II) ion, Cr+6 = chromium (IV) ionType III:
Use the element’s name with number of that element present by using Greek prefixes. Some other cations with their name are as follows.
2. Nomenclature of Anion Basics
In naming of anions, the root name of the element followed by suffix -ide
Cl-= chloride ion
S-2= sulphide ion
P-3 = phosphide ion
In case of Type III compounds a Greek prefix is added to the name of the second element. Here prefix denotes the number of elements present in compound.
- Mono $\to $ 1
- di $\to $ 2
- tri $\to $ 3
- tetra $\to $ 4
- penta $\to $ 5
- hexa $\to $ 6
- hepta $\to $ 7
- octa $\to $ 8
would be written as ‘A dioxide’. Remember the Greek prefix mono is never used for naming the first element of a compound and the final "o" or "a" of a prefix is dropped if the element begins with a vowel. There are some groups of atoms which behave as a single atom when it combines with another atom or group of atoms and called as radical or polyatomic ion.
For example, NO3-
are polyatomic ions which react intact in any reaction without get change in their formula or oxidation numbers of any of the elements and known as polyatomic ions. Some common anions and polyatomic ions with their name are as follow.
There are some common rules for addition of prefix and suffix.
- Suffix ‘-ate’ denotes the most common number of oxygen atoms like, sulphate (SO42-), chlorate (ClO3- ) and nitrate(NO3-).
- One less number of oxygen replace the ‘-ate’ suffix with ‘-ite’ in anions. For example, chlorite (ClO2-), sulphite (SO32-) and nitrite ion(NO2-).
- Compare to ‘-ate’ ion, one more oxygen added prefix ‘-per’, like permanganate, peroxide and perchlorate (ClO4-).
- In case of one less oxygen than in ‘-ite’ added prefix ‘hypo’. Like, hypochlorite.
- In cations, the ion with higher oxidation number added suffix ‘-ic’ anion with lower oxidation number added suffix ‘-ous’ to metal cation. For example, ferric ion is named as Fe3+ and Ferrous ion is Fe2+. Similarly Cu2+ is cupric ion and cuprous ion is named as Cu1+. By using the terms for cation and anions, we can write the name of chemical compound of all the three types.
, the name of the cation comes first followed by the name of the anion, which ended with suffix '–ide'
for monoatomic anions, while there will be no change in the name of polyatomic anions.
In type II
- BaCl2 = Bariumchloride
- LiNO3 = Lithium nitrate
- MgCO3 = Magnesium carbonate
- Na2SO4 = Sodium sulphate
- Al(NO3)3 = Aluminium nitrate
cases the oxidation state of metal cation is given by a roman numeral in parentheses.
In type III
- CuO = copper (II) oxide
- Cu2O = copper (I) oxide
- Cr2O3 = chromium (III) oxide
- HgI2 = Mercuric(II) iodide
compounds, the more positive atom is written first which located towards left and to the bottom of the periodic table followed by more negative second atom with suffix '-ide'
. The number of element indicates by the Greek roman letter in the compound.
For example, CO2
would be carbon dioxide. Other examples are P4
(tetraphosphorus decasulfide) and As2
(diarsenic penta-oxide). Some common chemical compounds with their name are as follow.
Nomenclature of Binary Compounds Those compounds which composed of two elements not with any polyatomic ions are called as binary compounds. For nomenclature of binary compounds, Name of compound started from the electropositive element which shows the positive oxidation number followed by the name of the electronegative element which has negative oxidation number with suffix ‘-ide’
. Binary compounds can be three types.
- Type I composed of metal (show only one oxidation number) and non-metal, Type II consists of metal (show more than one oxidation state) and Type III composed of two non-metals.
- In case of Type I binary compounds in the atom ratio determined by their oxidation numbers. In name of compound, metal will first followed by the non-metal with ‘-ide’ suffix.
- For example, HCl (hydrogen chloride), H2S (Hydrogen sulphide), NaCl (Sodium chloride), MgO (Magnesium oxide) etc.
- In case of Type II, the oxidation number of metal ion must be written in Roman numeral placed in parentheses following the name of the metal. For example; copper can have oxidation states of +1 and +2. Hence CuCl is named Copper (I) chloride, CuCl2 is named cooper (II) chloride.
- Similarly Iron can have oxidation states of +2 and +3. FeCl2 is named Iron(II) chloride and FeCl3 is named Iron(III) chloride.
- Type III binary compounds formed from two non-metals. Since there is no cation and anion in such type of binary compounds, therefore the electronegativity of elements is used for nomenclature of compounds.
- The element with the lowest electronegativity is named first followed by high electronegativity element with suffix ‘-ide’. For indicating the number of elements present in compounds, Greek prefix are used during naming of compound.
- Some common examples are CO (carbon monoxide), CO2 (carbon dioxide), PCl3 (phosphorus trichloride), PCl5 (phosphorus pentachloride), NO (nitrogen oxide), NO2 ( nitrogen dioxide ), N2O (dinitrogen monoxide), N2O3 ( dinitrogen trioxide) and N2O5 (dinitrogen pentoxide).
In one of the parallel method; instead of using numerical prefix, the oxidation numbers of the first element is written in parentheses. For example; Carbon dioxide can be written as Carbon (IV) oxide and Carbon monoxide can be written as carbon (II) oxide.
Some of the binary compounds are more frequently known by their common name.
Naming of Inorganic Bases Inorganic bases consist of metal ion with hydroxyl ion (-OH-) which is a polyatomic ion. Name of inorganic bases start from metal name followed by hydroxide. If metal ion can show more than one oxidation number, it is written in parentheses after metal ion name.
Naming of Acids
An acid contains hydrogen with a non-metallic element or with a polyatomic ion which has a negative oxidation number. There are some rules for nomenclature for inorganic acids.
- In an acid name replaces ‘-ate’ suffix with ‘-ic’ suffix, for example, sulfuric, chloric and nitric acid.
- ‘-ous’ suffix added to acid that contains the "-ite" form of the ion, like sulfurous, nitrous and chlorous acid.
- Prefix ‘hydro’ and suffix ‘-ic’ is used for acids whose anions contain no oxygen. For example, hydrochloric (HCl), Hydro sulfuric acid.
Some common examples of inorganic acids with their name are as follow.
Those inorganic acids which do not contain oxygen in polyatomic anion, their name started with a hydro- prefix and replaced the -ide
suffix with suffix -ic
. For example, HCl is named as hydrochloric acid, HF as hydrofluoric acid, HI as Hydroiodic acid and HBr as hydrobromic acid.
The polyatomic anions which contain oxygen are called as oxyanions.
There are many known oxyanions, like chlorine can bonded with oxygen in four different oxidation number to form four Oxyanions, ClO4−
For the nomenclature of oxyanions there are certain rules;
1. Most of the Oxyanions of elements are ended with suffix -ate.
- NO3- → Nitrate ion
- SO42- →Sulphate ion
- CO32- → Carbonate ion
- PO43- → Phosphate ion
- ClO3- → Chlorate ion
2. If oxyanion contains one less oxygen than the -ate oxyanion, the –ate suffix of oxyanion replaced by -ite.
- NO2- → Nitrite ion
- SO32- → Sulfite ion
- PO33- → Phosphite ion
- ClO2- → Chlorite ion
3. If oxyanion contains same charge but one more oxygen than the -ate oxyanion, prefix per- is added.
While in case of the presence of one less oxygen than the -ite oxyanion, the prefix hypo- is added.
- ClO4- → percholorate ion
- ClO3- → chlorate ion
- ClO2- → Chlorite ion
- ClO- → hypochlorite ion
A charged species or ion which composed of two or more covalently bonded atoms is called as polyatomic ion or molecular ion. For example, ammonium ion (NH4+
) is composed of five atoms, one nitrogen and four hydrogen atoms.
Similarly hydroxyl ion (-OH-
) and sulphate ion (
) are also example of polyatomic ions.
For the nomenclature of polyatomic ions, there are some important points to be considered.
No doubt these rules are not good for with all polyatomic ions, but they do work with the most common polyatomic ions like sulphate, phosphate, nitrate, chlorate ion. Some common polyatomic ions with their name are as follow.
- The prefix bi shows the addition of one hydrogen atom to the ion's formula and its charge is increased by 1. In place of bi-prefix, the word ‘hydrogen’ can be used. For example; CO32- is named as carbonate ion, and HCO32- is named as bicarbonate or hydrogen carbonate ion.
- Many of the common polyatomic anions are conjugate bases of inorganic acids, like SO42- ion derived from H2SO4.
- Oxyanions are very common polyatomic ions which are named according to the number of oxygen present in oxyanion.
Some chemicals compounds adsorb water from atmosphere and water will form a complex in which water generally bonds with the cation in ionic substances. Such type of water is called as water of hydration or water of crystallization
The amount of water present as water of hydration is present in stoichiometric amounts and written as component of compounds separated by dot. Hydrate compounds are named by stating the name of the anhydrous component followed by the Greek prefix which specifies the number of moles of water present followed by word hydrate. There are certain rules for nomenclature of hydrate compounds.
- First the name of ionic compound is written according to rules for naming of ionic compounds. For example; MgSO4•7H2O is named as magnesium sulphate.
- The term ‘hydrate’ added after the name of ionic compound with Greek prefix indicates the number of water molecule bonded with one mole of ionic compound. So MgSO4•7H2O would be magnesium sulphate octa hydrate.
- The formula of ionic compound is separated from water of hydration by a centered dot. Hydrate salts are batter known with their common names.
Some common examples of hydrate salts with their name are as follow.