| You should have a
list from your lecture class which contains a list of the ions you need
to know. There are also lists of cations and anions on the left
side of this page under "Resources". Essentially, you have to memorize this list.
Here are some tips which may help you memorize the list...
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Monatomic Cations - Groups 1A and 2A plus Aluminum |
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The names of these cations are exactly the same as the names of the
elements.
The charges for these metal cations can be predicted
based on where they are on the Periodic Table. The positive charge
will correspond to the number of spots away the nearest noble gas
is.
Examples:
Sodium is one spot past the nearest noble gas, so
sodium ion has a 1+ charge (Na1+).
Aluminum is three
spots past the nearest noble gas, so aluminum ion has a 3+ charge (Al3+). |
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Monatomic Transition Metal Cations |
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These are a little trickier. Many,
but not all of them, have more than one possible ion that they
form. You also cannot tell what the charge is from looking at the
Periodic Table.
The names of those metal cations for which there
is more than one choice will include a Roman numeral indicating the
charge. For example Pb4+ is lead(IV) and Pb2+
is lead(II). You must consult your list of ions to know what the
charges are and which transition metals have more than one ion.
Some transition metals have only one ion, in which case the Roman
numeral is not used. For example, silver (Ag1+) and zinc
(Zn2+).
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Polyatomic Cations |
There are usually only two polyatomic cations used
in this class (consult your ion sheet to be sure). One is
ammonium, NH41+ and the other is mercury(I), Hg22+.
In both cases, the polyatomic ion consists of several atoms bonded
together in a particular way, and must always remain intact as the
grouping of atoms when combined with an anion to make an ionic compound.
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Monatomic Anions - Nonmetals |
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These come from the
nonmetal atoms on the Periodic Table. Their names are the names of
the elements, with the ending changed to -ide.
Their
charges can be predicted based on where they are on the Periodic
Table. The negative charge will correspond to the number of spots
away the nearest noble gas is.
Examples:
chlorine is one spot from the next noble gas, so chloride
has a 1- charge (Cl1-).
Sulfur is two spots away from the next noble gas, so sulfide has a
2- charge (S2-). |
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Polyatomic Anions |
There are many polyatomic anions to
learn. It may be easiest to simply memorize the list.
However, there are a few patterns which are pointed out here.
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Polyatomic Anions: ate vs ite |
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For cases where an atom combines with oxygen in two
different ways to form two different ions, generally to two ions have
the same charge. The name of the ion with more oxygen ends in -ate
and the name of the ion with less oxygen ends in -ite.
Examples:
| SO32- |
sulfite |
|
SO42- |
sulfate |
| HSO31- |
hydrogen sulfite
(or bisulfite) |
|
HSO42- |
hydrogen sulfate
(or bisulfate) |
| NO21- |
nitrite |
|
NO31- |
nitrate |
|
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Polyatomic Anions: per-ate vs ate vs ite vs hypo-ite |
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Chlorine, bromine and iodine each combine with
oxygen to form four different ions, all with a 1- charge. The
ion with 1 oxygen has a prefix of hypo- and ends in -ite.
The ion with 2 oxygens simply ends in -ite. The ion with
3 oxygens simply ends in -ate. And the ion with 4 oxygens has a
prefix of per- and ends in -ate.
Examples:
| ClO1- |
hypochlorite |
|
BrO1- |
hypobromite |
|
IO1- |
hypoiodite |
| ClO21- |
chlorite |
|
BrO21- |
bromite |
|
IO21- |
iodite |
| ClO31- |
chlorate |
|
BrO31- |
bromate |
|
IO31- |
iodate |
| ClO41- |
perchlorate |
|
BrO41- |
perbromate |
|
IO41- |
periodate |
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Polyatomic Anions: Anions With Hydrogen Added... |
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Some anions containing oxygen can be modified by adding
one or more hydrogens to them. The hydrogen added is in the form
of H+. It is put onto the beginning of the ion formula.
The charge of the new ion is equal to the sum of the charges of the
old ion and the added hydrogen ions.
To name the new ion, add
the word "hydrogen" to the beginning of the old ion name (or
use a prefix "bi-" instead). When two hydrogens are
added, use "dihydrogen" instead.
Examples:
| CO32- |
carbonate |
|
HCO31- |
bicarbonate or hydrogen carbonate |
| SO32- |
sulfite |
|
HSO31- |
bisulfite or hydrogen sulfite |
| SO42- |
sulfate |
|
HSO41- |
bisulfate or hydrogen sulfate |
| PO43- |
phosphate |
|
HPO42- |
hydrogen phosphate |
|
H2PO41- |
dihydrogen phosphate |
Note that when the hydrogens are added, there still must be an overall
charge. If there were not still an overall charge, then you
would have an acid (a compound), not an ion. Then, the naming
rules would be different.
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Polyatomic Anions: Anions With Sulfur in Place of
Oxygen... |
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Some anions have a sulfur atom replacing an oxygen atom. The ion
is named by putting "thio" in front of the name of the original ion.
Examples:
| SO42- |
sulfate |
|
S2O32- |
thiosulfate |
| OCN1- |
cyanate |
|
SCN1- |
thiocyanate |
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