Polyatomic ion

From Free net encyclopedia

Revision as of 20:02, 21 April 2006; view current revision
←Older revision | Newer revision→

A polyatomic ion is an ion consisting of a molecule with covalently bonded atoms or of a metal complex that can be considered as acting as a single unit in the context of acid and base chemistry or in the formation of salts. The prefix poly- means many in Greek. Note, a polyatomic ion is also referred to in older works as a radical. In current usage the term radical refers to free radicals which are uncharged species with an unpaired electron. Some can be used in decomposition reactions, providing spectacular results, such as H{{#if:{{{1|}}}|2}}O{{#if:{{{1|}}}|2|}} and iodine.

Hydroxide Ions and Ammonium Ions

  • A Hydroxide ion is made of one oxygen ion and one hydrogen ion: its chemical formula is (O{{#if:{{{1|}}}|{{{1}}}|}}H{{#if:{{{1|}}}|{{{1}}}}})-. It has a negative charge.
  • An Ammonium ion is made up of one nitrogen atom and four hydrogen atoms: its Chemical Formula is (N{{#if:{{{1|}}}|{{{1}}}|}}H{{#if:{{{1|}}}|4}})+. It has a positive charge.

A large polyatomic ion will often be considered as the conjugate acid or conjugate base of a neutral molecule, for example the conjugate acid of adrenaline at the amine group.

Note that many of the common negatively-charged anionic polyatomic ions are conjugate bases of acids derived from the oxides of non-metallic elements. For example the sulfate or S{{#if:{{{1|}}}|{{{1}}}|}}O{{#if:{{{1|}}}|4|}}2- ion is derived from H2SO4 which can be regarded as SO3 + H2O.

There are two "rules" that can be used for making the learning of polyatomic ions somewhat easier. First, when the prefix bi- is added to a name, a hydrogen is added to the ion's formula and its charge reduced by 1. This reduction is a function of the hydrogen ion being a +1 charge. An alternate to the bi- prefix is to use the word hydrogen in its place.

Example:

carbonate becomes bicarbonate or hydrogen carbonate

C{{#if:{{{1|}}}|{{{1}}}|}}O{{#if:{{{1|}}}|3|}}2- becomes H{{#if:{{{1|}}}|{{{1}}}}}C{{#if:{{{1|}}}|{{{1}}}|}}O{{#if:{{{1|}}}|3|}}-

The second rule looks at the number of oxygens in an ion. Consider the chlorate family:

perchlorate Cl{{#if:{{{1|}}}|{{{1}}}|}}O{{#if:{{{1|}}}|4|}}-
chlorate Cl{{#if:{{{1|}}}|{{{1}}}|}}O{{#if:{{{1|}}}|3|}}-
chlorite Cl{{#if:{{{1|}}}|{{{1}}}|}}O{{#if:{{{1|}}}|2|}}-
hypochlorite Cl{{#if:{{{1|}}}|{{{1}}}|}}O{{#if:{{{1|}}}|{{{1}}}|}}-

First, think of the -ate ion as being the "base" name, in which case the addition of a per- prefix adds an oxygen. Changing the -ate suffix to -ite will reduce the oxygens by one, and replacing the -ate and adding the prefix hypo- reduces the number of oxygens by two. In all situations, the charge is not affected.

It is important to note that these rules will not work with all polyatomic ions, but they do work with the most common ones (sulfate, phosphate, nitrate, chlorate).

The most common type of file to veiw ion representations is a PDB which refers to Protein Databank. There are also now other kinds becoming available including CIF.

Common polyatomic ions

Common polyatomic ions
acetate CH3COO- or C2H3O2-
aluminate AlO2-, Al2O4-2
amide NH2-
ammonium NH4+
arsenate AsO4-3
arsenite AsO3-3
azide N3-
bicarbonate (hydrogen carbonate) HCO3-
tetraborate B4O7-2
bromate BrO3-
bromite BrO2-
carbide C2-2
carbonate CO3-2
chlorate ClO3-
chlorite ClO2-
chromate CrO4-2
chromite CrO2-
chromyl CrO2+2
citrate C6H5O7-3
cyanate OCN-
cyanide CN-
dichromate Cr2O7-2
dihydrogen arsenate H2AsO4-
dihydrogen phosphate H2PO4-
dihydrogen phosphite H2PO3-
dioxygenyl O2+
disulfide S2-2
ferricyanide Fe(CN)6-3
ferrocyanide Fe(CN)6-4
formate (formiate) HCO2-
fulminate CNO-
hydrogen arsenate HAsO4-
hydrogen carbonate (bicarbonate) HCO3-
hydrazide N2H3-
hydrogen phosphate HPO4-2
hydrogen phosphite HPO3-2
hydrogen sulfate HSO4-
hydrogen sulfite HSO3-
hydronium H3O+
hydroxide OH-
hypobromite BrO-
hypochlorite ClO-
hypoiodite IO-
hypophosphite PO2-3
iodate IO3-
iodite IO2-
isocyanate NCO-
Mercury Hg2+2
molybdate MoO4-2
nitrate NO3-
nitrite NO2-
oxalate (COO)2-2
ozonide O3-
perbromate BrO4-
perchlorate ClO4-
periodate IO4-
permanganate MnO4-
peroxide O2-2
phosphate PO4-3
phosphite PO3-3
pyridinium C5H5NH+
pyrophosphate P2O7-4
quaternary ammonium NR4+
selenate SeO4-2
silicate SixOy
sulfate SO4-2
sulfite SO3-2
sulfonium R3S+
superoxide O2-
tartrate (CH(OH)COO)2-2
thiocyanate CNS-
thiosulfate S2O3-2
tosylate (toluenesulfonate) CH3C6H4SO3-
triflate (trifluoromethanesulfonate) CF3SO3-
tungstate WO4-2
uranyl UO+2
vanadate VO3-
vanadyl(IV) VO+2
Vanadyl(V) VO2+

See also

External links

[http://en.wikipedia.org/wiki/Protein_Data_Bank.html PDB information]fr:ion polyatomique pt:Íon poliatômico