Compounds
Atoms of the same or different elements can combine in set proportions to form compounds. The proportions are determined by the numbers of electrons shared or exchanged between elements.
This combining power of elements is most readily learned by memorizing each element's common charge or valence. You can think of valence as something similar to a connecting link for building blocks. Some atoms only can form one link with other atoms while others may form multiple links.
Naming Ionic Compounds
We can learn the nomenclature of common ionic inorganic compounds by
memorizing the following tables of common ions.
Sometimes clusters of
atoms are called groups and we learn a
charge for the group as a whole. The order of the letters in a group should be
maintained when writing the formula.
The elements and groups with positive charges (cations) are written and named first as in the case of LiF, lithium fluoride and NH4Cl, ammonium chloride.
Note that some metals have
more than one common charge and we use a
Roman Numeral to designate which ion is present in the compound such as iron(III)...read
as iron 3. If a metal only has one common charge, the Roman Numeral is not used.
The anions that are formed from single atoms are named by
dropping the elemental suffix and adding "-ide".
The overall charge of an ionic compound should be zero.
When you combine atoms or groups to form a compound, the key is to make sure
that the overall charges are balanced.
There is a clever way to arrive at the formula when you have
elements or groups that have different charges. Use the charge of each
element or group as the subscript for the other element or group as shown in
the following animation.
|
+1 charge |
+2 charge |
+3 charge |
+4 charge |
|
H+ hydrogen |
Ca2+ calcium |
Al3+ aluminum |
Si4+ silicon |
|
Li+ lithium |
Be2+ beryllium |
Fe3+ iron(III) |
Sn4+ tin(IV) |
|
K+ potassium |
Ba2+ barium |
|
Pb4+ lead(IV) |
|
Na+ sodium |
Cu2+ copper(II) |
|
|
|
Ag+ silver |
Fe2+ iron(II) |
|
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|
Cu+ copper(I) |
Mg2+ magnesium |
|
|
|
NH4+ ammonium |
Zn2+ zinc |
|
|
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|
Sn2+ tin(II) |
|
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|
Hg2+ mercury(II) |
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Ni2+ nickel |
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Pb2+ lead(II) |
|
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Table of Anions
|
-1 charge |
-2 charge |
-3 charge |
-4 charge |
|
F- fluoride |
O2- oxide |
PO43- phosphate |
C4- carbide |
|
Cl- chloride |
S2- sulfide |
P3- phosphide |
|
|
Br- bromide |
CO32- carbonate |
N3- nitride |
|
|
I- iodide |
SO42- sulfate |
|
|
|
OH- hydroxide |
HPO42- hydrogen phosphate |
|
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|
CN- cyanide |
|
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HCO3- bicarbonate* |
|
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NO2- nitrite |
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NO3- nitrate |
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CH3CO2- acetate |
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H2PO4- dihydrogen phosphate |
|
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HSO4- hydrogen sulfate |
|
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|
* The name "bicarbonate" is actually a common name. It is given here because it is so commonly used. The proper chemical name for this group is "hydrogen carbonate". Sometimes it is hard to know what a substance is from the common name.
Examples of Ionic Inorganic Compounds
Try to figure out the name or
formula and then click on the formula or name to see the correct answer.
Naming Molecular Compounds
Most elements can be drawn by just using the symbols. However, the most stable form for many elements is a compound rather than the individual atom. The most common examples of these binary (2 atom) compounds are shown in the following table.
| hydrogen | H2 |
| nitrogen | N2 |
| oxygen | O2 |
| fluorine | F2 |
| chlorine | Cl2 |
| bromine | Br2 |
| iodine | I2 |
The non-ionic
inorganic compounds (molecular inorganic compounds) are similar to these
compounds but are combinations of two or more nonmetallic
elements. Most of these compounds are combinations of elements from Groups IVA
to VIIA with one another or with hydrogen.
When a hydrogen atom forms compounds with the nonmetals, the hydrogen atom is named first and the nonmetal is named as if it were a negative ion.
| HF (g) | hydrogen fluoride...The (g) for (gas state) must be shown since HF in a solution of water is called hydrofluoric acid. This is also done with HCl, HBr and HI. They are all in the same family. |
| H2S (g) | hydrogen sulfide...In a water solution this would be called hydrosulfuric acid. |
The following compounds are exceptions to this rule...
| H2O | water...It is not known as dihydrogen oxide. |
| NH3 | ammonia...It is not known as trihydrogen nitride. |
| CH4 | methane...The compounds composed of carbon have their own special names. |
When other elements combine to form binary compounds, the formula is usually written by putting the elements in order of increasing group number.
The number of atoms is given by a prefix, such as "mono", "di", "tri", "tetra", "penta", "hexa", "hepta" and "octa"...for 1, 2, 3, 4, 5, 6, 7 and 8.
Always use the entire prefix except for monooxide...which is named monoxide.
Never use the mono prefix for the first element and always use a prefix for the second element.
| CO | carbon monoxide |
| NO | nitrogen monoxide |
| N2O | dinitrogen monoxide...laughing gas |
| PCl3 | phosphorus trichloride |
| CCl4 | carbon tetrachloride |
Examples of Molecular Inorganic Compounds
Try to figure out the name or formula and then click on name or the formula to check your answer.
Deciding
Which Nomenclature Rules to Follow
1. Determine whether the
compound is an ionic compound or a molecular compound.
If a metal is present, the compound is an ionic compound for the purposes of this course. If no metal is present, the compound is a molecular compound.
If the ammonium ion, NH4+ is present, the compound is ionic.
2. If the compound is
ionic, use the names and charges given in the tables.
3. If the compound is a molecular compound, use the rules for naming binary molecular compounds.
Return to Inorganic Chemistry Tutorials
Copyright © January 2001 by
Richard C. Banks...all rights reserved.