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17, Monoatomic and polyatomic anions and cations (A. Peterson)
Added by Mary Blackwell, last edited by April Peterson on Nov 02, 2007

Monoatomic ions

Monoatomic anions are non-metal elements with a negative charge. Monoatomic cations are metallic ions with a positive charge. These elements tend to lose their electrons, forming cations. The metals in groups 1, 2 and 3 loose their electrons in predictable ways in that they loose as many electrons as the group they're in. Ex. by looking at the periodic table below you can see that Li (group 1) gains a charge of +1, Be (group 2) +2 and Sc (group 3) +3. Also when looking at the periodic table you can see that some metals have more than one cation, Fe mainly Cu. With these two you can tell which version it is by the charge. Ex. Fe +3 is iron III.

Many monoatomic ions make up electrolyte solutions essential to biological functions.

When metals lose an electron to a non-metal they form an ionic bond. The names of monoatomic anions are determined by adding ide to the root. Ex. the hydrogen ion (H - ) is called hydride. Naming cations is a little simpler, in ionic compounds the cation name is always first, and it is just the name of the metal.

from http://www.mpcfaculty.net/mark_bishop/monatomic_ion_configurations.htm
a periodic table with the charges for monoatomic ions.

Polyatomic ions

Essentially polyatomic ions charged molecules. Each atom in a polyatomic ion is held together by a covalent bond (sharing electrons), and acts as a single unit and retains it's chemical properties. "Polyatomic ions are charged because they have fewer or more electrons than are needed to balance the positive charges of the nuclei present in the ion" (cartage.org).

from, http://en.wikipedia.org/wiki/Ionic_bond
This animation illustrates what happens when an ionic bond forms. Na, loses an electron to have a valence shell of 8 electrons, and becomes a cation. Cl takes the electron and to also form a valence shell of 8 and becomes a anion. The negative charges of the cation and anion attract to form the ionic bond.

+1   -1   -2   -3  
NH 4 + ammonium C 2 H 3 O 2 - acetate CO 3 -2 carbonate PO 4 -3 phosphate
H 3 O + hydronium CN - cyanide CrO 4 -2 chormate  

here's a table of some polyatomic ions, for a complete list of the basic polyatomic ions visit this web site, [http://www2.pvc.maricopa.edu/tutor/chem/chem130/nomenclature/polyatomicion.html ]
polyatomic cations besides ammonium, hydronium and mercury I are very rare and usually not found in basic chemistry.

Naming polyatomic ions can be a little tricky. Depending on what atoms are added to the molecule the different prefixes and suffixes are added.

from, http://www.caton.org/images/chem/TableF.gif
This table illustrates how prefixes and suffixes are added to the base
polyatomic ions ending with ate are considered the "base", the suffix ite indicates that an oxygen has been removed, hypo means that 2 oxygen have been removed, and pre means that an oxygen has been added.



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