Naming Inorganic Compounds
With over 10 million known chemicals, and potentially dangerous results if chemicals are combined in an incorrect manner, imagine the problem if you are in the lab and say "mix 10 grams of that stuff in with this stuff". We need to be very clear on identification of chemicals.
Two early classifications of chemical compounds:
Organic compounds. These contain the element Carbon (C). "Life on earth is carbon
based"Inorganic compounds. All other compounds
Organic compounds were associated with living organisms, however, a large number of organic compounds have been synthesized which do not occur in nature, so this distinction is no longer valid.
Ionic compounds: (an association of a cation and an anion)
The positive ion (cation) is always named first and listed first in writing the formula for the compound.
The vast majority of monatomic (composed of a single atom) cations are formed from metallic elements:
Na+ Sodium ionZn2+ Zinc ionAl3+ Aluminum ion
If an element can form more than one positive ion, the positive charge of the ion is indicated by a Roman numeral in parentheses following the name of the metal:
Fe2+ iron(II) ionFe3+ iron(III) ionCu+ copper(I) ionCu2+ copper(II) ion
Iron and copper are examples of transition metals. They occur in the block of elements from IIIB to IIB of the periodic table.
The transition metals often form two or more different monoatomic cations.
click on picture for larger image
An older nomenclature for distinguishing between the different ions of a metal is to use the suffixes -ous and -ic. The suffix -ic will indicate the ion of higher ionic charge:
Fe2+ ferrous ionFe3+ ferric ionCu+ cuprous ionCu2+ cupric ion
Note that the different ions of the same element often have quite different chemical properties (again, pointing to the importance of electrons in determining chemical reactivity).
Ionic compounds: Anions
Monatomic anions are usually formed from non-metallic elements. They are named by dropping the ending of the element name and adding -ide:
Cl- chloride ionF- flouride ionS2- sulfide ionO2- oxide ion
Some common polyatomic anions include:
OH- hydroxide ionCN- cyanide ion
Many polyatomic anions contain oxygen, and are referred to as oxyanions. When an element can form two different oxyanions the name of the one that contains more oxygen ends in -ate, the one with less ends in -ite:
NO2- nitrite ionNO3- nitrate ionSO32- sulfite ionSO42- sulfate ion
Note that unlike the -ous and -ic suffix nomenclature to distinguish the different cations of a metal, the -ite and -ate suffix is used to distinguish the relative amounts of the oxygen atoms in a (polyatomic) oxyanion (in the above examples the ionic charge is the same for the -ite and -ate ions of a specific oxyanion).
Now to get really perverse....
Some compounds can have multiple oxyanion forms (the oxyanions involving the halogens, for example):
ClO-ClO2-ClO3-ClO4-
Note again, that the number of Oxygens relative to the Chlorine is changing, but that the ionic charge is not.
How do we name these? The -ite and -ate suffixes are still used, but we have to add an additional modification to allow us to distinguish between the four forms:
ClO- hypochlorite ionClO2- chlorite ionClO3- chlorate ionClO4- perchlorate ion

It should be pointed out that some of the naming of ions is historical and is not necessarily systematic. It may be frustrating and confusing, but its all part of chemistry's rich history.
Many polyatomic anions that have high (negative) charges can add one or more hydrogen cations (H+) to form anions of lower effective charge. The naming of these anions reflects whether the H+ addition involves one or more hydrogen ions:
HSO4- hydrogen sulfate ionH2PO4- dihydrogen phosphate ion
Acids
An acid is a substance whose molecules yield hydrogen (H+) ions when dissolved in water.The formula of an acid consists of an anionic group whose charged is balanced by one or more H+ ions.The name of the acid is related to the name of the anionAnions whose names end in -ide have associated acids that have the hydro- prefix and an -ic suffix:
Cl- chloride anion
HCl hydrochloric acid
S2- sulfide anion
H2S hydrosulfuric acid
Using the -ic suffix here may seem a bit inconsistent since it was used in naming metal cations to indicate the form which had the higher positive charge. However, when you think about it, the acid compound has a higher net positive charge than the anion from which it is derived (the anion is negatively charge and the associated acid is neutral).
Again, things get complicated when we consider the acids of oxyanions:
If the anion has an -ate ending, the corresponding acid is given an -ic endingIf the anion has an -ite ending, the corresponding acid has an -ous ending.Prefixes in the name of the anion are kept in naming the acid
ClO- hypochlorite ion
HClO hypochlorous acid
ClO2- chlorite ion
HClO2 chlorous acid
ClO3- chlorate ion
HClO3 chloric acid
ClO4- perchlorate ion
HClO4 perchloric acid
This is confusing: we previously had used the -ous and -ic suffixes to indicate the ionic charge differences in metal cations (-ic had a higher positive charge). Although in comparison to the ionic form, the -ic and -ous acid forms have a higher net positive charge, the -ic suffix would indicate forms with a higher oxygen content, and not an apparent charge difference.
Molecular compounds
Although they may not be ionic compounds, chemically bonded compounds of two different elements can be thought of as being made up of an element with a more positive chemical nature, and one that has a more negative nature in comparison. Elements on the left hand side of the periodic table prefer to donate electrons (thus taking on a more positive chemical nature), and elements on the right hand side prefer to accept electrons (thus taking on a more negative chemical nature). The element with the more positive nature in a compound is named first. The second element is named with an -ide ending.
Often a pair of elements can form several different molecular compounds. For example, Carbon and Oxygen can form CO and CO2. Prefixes are used to identify the relative number of atoms in such compounds:
CO carbon monoxide (carbon mono oxide)CO2 carbon dioxide
Such prefixes can extend for quite a way for some organic and polymeric compounds (a common detergent in shampoos is sodium dodecylsulfate, or "SDS", also known as Sodium Laurel Sulfate because it sounds more benign and holistic). The list of such prefixes includes:
Prefix & Meaning
Mono-1
Di-2
Tri-3
Tetra-4
Penta-5
Hexa-6
Hepta-7
Octa-8
Nona-9
Deca-10
Undeca-11
Dodeca-12
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