How It Works - Ions And Ionization - Cations, Anions, Elements And ...

ANIONS.

When a neutrally charged atom gains electrons, acquiring a negative charge as a result, this type of ion is known as an anion (AN-ie-un). Anions can be represented symbolically in much the same way as cations: Cl − , for A COMMON FORM OF FIELD IONIZATION IS STATIC ELECTRICITY . H ERE , A GIRL PLACES HER HAND ON A STATIC ELECTRICITY GENERATOR . ( Paul A. Souders/Corbis . Reproduced by permission.) instance, is an anion of chlorine that forms when it acquires an electron, thus assuming a net charge of −1. Note that the 1 is not represented in the superscript notation, much as people do not write 10 1 . In both cases, the 1 is assumed, but any number higher than 1 is shown.

The anion described here is never called a chlorine anion; rather, anions have a special nomenclature. If the anion represents, as was the case here, a single element, it is named by adding the suffix -ide to the name of the original element name: chloride. Such is the case, for instance, with a deadly mixture of carbon and nitrogen (CN − ), better known as cyanide.

Most often the-ide suffix is used, but in the case of most anions involving more than one element (polyatomic anions), as well as with oxyanions (anions containing oxygen), the rules can get fairly complicated. The general principles for naming anions are as follows:

• -ide: A single element with a negative charge. Note, however, that both hydroxide (OH − ) and cyanide (CN − ) also receive the-ide suffix, even though they involve more than one element.
• -ate: An oxyanion with the normal number of oxygen atoms, a number that depends on the nature of the compound. Examples include oxalate (C 2 O 4 −2 ) or chlorate (ClO 3 − ).
• -ite: An oxyanion containing 1 less oxygen than normal. Examples include chlorite (ClO 2 − ).
• hypo____ite: An oxyanion with 2 less oxygens than normal, but with the normal charge. An example is hypochlorite, or ClO − .
• per____ate: An oxyanion with 1 more oxygen than normal, but with the normal charge. Perchlorate, or ClO 4 − , is an example.
• thio-: An anion in which sulfur has replaced an oxygen. Thus, SO 4 −2 is called sulfate, whereas S 2 O 3 −2 is called thiosulfate.