Naming Rules for Ions

8/10/2019 Naming Rules for Ions

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iron forms Fe3+

as well Fe2+

chromium forms Cr 3+

more easily than Cr 2+

note that mercury forms two kinds of 2+ ions but that one of the ions consists of 2Hg atoms bonded together

NAMING: The atomic cations are named just like the neutral element followed by the word ion:For example: K + is the potassium ion

MULTIVALENT IONS: To distinguish the atomic ions Fe3+

from Fe2+

we name them iron(III)ion

and iron(II) ion, respectively, or Fe(III) ion

and Fe(II). Similarly for copper(II) ion and

copper(I) ion. In an older method (see page 59 of Burdge), the ending -ic is used for the higher of

two possible charge states and -ous for the lower [this method is widely used by practicing (readolder ) chemists but is not encouraged because it can’t handle an atom with more than 2 common

charge states]

C. Anions - These are the simplest negative ions, consisting of a single atom of a given element

in its most common negative charge state. We only consider the non-metals in this namingscheme. Use the root of the element’s name and add -ide to get the name of the most common

anion.

Examples are:

(1st row): H

- is the hydr ide ion

(2nd

row): N3-

is the nitr ide ion ; O2-

is the oxide ion ; F- is the fluor ide ion

(3rd

row): P3-

is the phosphide ion; S2-

is the sulf ide ion; Cl- is the chlor ide ion

II. Molecular ions

These are generally made up of a collection of nonmetal atoms bonded together but that are

stable with a net charge.

A.Cations -- The only significant positive molecular ion is NH4+, the ammonium ion

B. Anions

1. A few polyatomic anions have names that end in -ide like the atomic anions:

OH- is hydroxide, CN

- is cyanide, O2

2-is peroxide

2. Oxyanions -- These are anions consisting of a non-metal atom such as carbon acting as a

center to which one or more oxygen atoms are bonded. A very common example is the carbonate ion, CO3

2-which looks like this:



The table below shows a number of elements acting as a central atom with in some cases up to

four different common oxyanions (the chlorine series). One of these ions (which we shall

consider to be the most common) is named with the central atom’s root and the ending -ate. Theoxyanion in the series with one less oxygen has the ending -ite. If the series continues down with

one less oxygen than this we use the prefix hypo- (short for less than). If the series has an

oxyanion with one more oxygen than the -ate ion we add the prefix per- (short for hyper or morethan).

MEMORIZE THE IONS IN THIS TABLE WHICH HAVE THE -ate ENDING

Central atom C N P S Cl Mn

per- -ate ClO4- MnO4

-

-ate CO32-

NO3- PO4

3- SO4

2- ClO3

- MnO3

-

-ite NO2- PO3

3- SO3

2- ClO2

-

hypo- -ite ClO-

Notice that in each column, the charge remains the same even as the number of oxygens bondedto the central atom changes.

Also note that the six ions I've asked you to memorize can also help with other members of the

same family: the bromate ion is analogous to the chlorate ion for example.

III. Acids

An acid gives off or yields hydrogen ion, H+ when it is dissolved in water:

HCl (aq) -- > H+ (aq) + Cl

-(aq)

The naming of the acids depends on the name of the corresponding anion.



Anions named with -ide:

chlor ide ion corresponds to hydrochlor ic acid

cyanide ion corresponds to hydrocyanic acid

Anions named with -ate and so forth (oxyanions)

Chlor ate ion corresponds to chlor ic acid

Chlor ite ion corresponds to chlor ous acid

Now, what about per chlor ate ion? per chlor ic acid

hypochlor ite ion? hypochlor ous acid

IV. Ionic compounds

Simply start with the name of the metal and add the name of the anion of the non-metal

The most common example is

NaCl (s) or sodium chloride.

How about BaSO4? barium sulfate

Or FeO? iron(II) oxide

See Table 2.9 on page 60 in Burdge for some more examples.

V. Binary molecular compounds

These are compounds made up of two non-metals. We write the element belonging to the lower

group number first, then the other element with the ending -ide and we use prefixes like mono-, di-, tri- to say how many of each atom are in the compound. A more complete table of these

prefixes is given in Table 2.2 of Burdge on page 52.

Examples (more on page 52):

NO is nitrogen oxide

N2O is dinitrogen oxide

P2O5 is di phosphorus pentoxide

Naming Rules for Ions

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