Ions
Polyatomic ions
Salts |
Common salt is the best known example of the large, important group
of compounds known collectively as "salts". Sodium chloride
displays many of the properties associated with salts and, in many ways,
is a typical salt. Like all salts, sodium chloride is composed of innumerable
individual ions forming a giant ionic crystal lattice, commonly called
a salt crystal. The topic, NaCl,
sodium chloride or common salt should be read in conjunction with
this topic.
Ions
Ions are formed when atoms or molecules gain or lose electrons. Only the
outermost electrons of an atom can be removed or added to during chemical
reactions, which limits the types of ions that can be formed. Most common
ions are limited to charges between plus or minus 3.
When an atom or molecule loses electrons, it becomes positively charged. The size of the charge is dependent on the number of electrons lost. The sodium atom loses one electron to form a 1+ ion, while aluminium can loses 3 electrons to form a 3+ ion.
Negative ions are formed when atoms gain electrons. The size of the charge is again dependant on the number of electrons gained. The chlorine atom gains one electron to form the chloride ion, Cl- ion, while oxygen gains two electrons to form the oxide ion, O2-.
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Formation of a calcium ion |
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Formation of a chloride ion |
Below is a table of common ions, listed by charge.
|
+1
|
+2
|
+3
|
-1
|
-2
|
-3
|
|
hydrogen |
magnesium
Mg2+ |
aluminium
Al3+ |
hydride
H- |
oxide
O2- |
nitride
N3- |
|
sodium
Na+ |
calcium
Ca2+ |
iron(III)
Fe3+ |
fluoride
F- |
sulfide
S2- |
phosphide
P3- |
|
potassium
K+ |
copper(II)
Cu2+ |
chloride
Cl- |
sulfate
SO42- |
phosphate
PO43- |
|
|
copper(I)
Cu+ |
cobalt(II)
Co2+ |
bromide
Br- |
sulfite
SO32- |
||
|
iodide
I- |
Note: when
a metal atom can form more than one positive ion, the charge on the ion
is given by Roman Numerals in brackets. The negative ions of non-metals
lose the ending of the atom's name and replace it with the letters -ide.
Polyatomic ions containing oxygen end in -ite and
-ate.
Polyatomic
ions
Molecules can also form ions, usually by gaining electrons
and forming negative ions. Electrically charged molecules are known as
polyatomic ions, literally "many atomed ions". Although larger
than most monatomic ions (those composed of only one ion), polyatomic
ions behave in the same way as other ions in forming salts with positive
ions.
Salts
Salts are formed when positive and negative ions come together in
giant ionic crystal lattices in ratios that give the overall crystal a
zero charge. In other words, the total charge of all the positive ions
equals the total charge of the negative ions. See the topic Making
salts - the rules of electrovalency for more information on how salts
form crystals and Ionic
crystals - salts for the properties of giant ionic crystals.
| Copyright owned by the State of Victoria (Department of Education and Early Childhood Development). Used with Permission. |  |
