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Hydroxide Ions and Ammonium Ions
  • A Hydroxide ion is made of one oxygen ion and one hydrogen ion: its chemical formula is ()-. It has a negative charge.

  • An Ammonium ion is made up of one nitrogen atom and four hydrogen atoms: its Chemical Formula is ()+. 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 Anion ic polyatomic ions are conjugate bases of acids derived from the Oxide s of non-metallic elements. For example the Sulfate or 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

2- becomes -

The second rule looks at the number of oxygens in an ion. Consider the chlorate family:
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 view ion representations is a PDB which refers to Protein Databank. There are also now other kinds becoming available including CIF.


COMMON POLYATOMIC IONS



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PDB information]