Naming Compounds And Determining Formulas (Page 3 of 3) in pdf

Nonbinary compounds (more than two elements)

Ionic compounds consisting of a metal cation and a polyatomic anion: metal name followed by polyatomic

anion name. Sounds too easy, doesn’t it? The trick is in knowing the names of the polyatomic ions.

There is a list of them in the book for sure, but you don’t have to memorize every last one.

For the oxoanions (the ones ending in “O

”), memorize the “ate” formula and the charge. Then you can

follow these rules:

The charge on the other ions composed of the same two elements is the same. Yep. It’s true.

The ion with one less oxygen atom uses the “ite” ending instead of “ate.”

If there are two fewer oxygens, keep the “ite” and add the “hypo” prefix. This is unusual, but there are

some. If you know this rule, you don’t have to know which ones can have two fewer oxygens.

If there’s one more oxygen than the “ate,” add the “per” prefix and keep the “ate.” As with

“hypo<root>ite,” this is also uncommon.

Some examples:

is the sulfate ion.

is the sulfite ion (one less oxygen).

There are no SO

or SO

ions, so there are no hyposulfite or persulfate ions. (There is a hyposulfate, it

isn’t of the SO

family.)

ClO

is chlorate ion.

ClO

is chlorite ion.

ClO

is hypochlorite ion.

ClO

is perchlorate ion.

is nitrate ion.

is nitrite ion.

With all the oxoanions, the endings change when they are combined with hydrogen (acids). The name of

the oxoanion is changed as follows. Anywhere you see “ate,” change “ate” to “ic.” Similarly, “ite” becomes

“ous.” Prefixes don’t change.

is sodium sulfate, and H

is sulfuric acid.

is sodium sulfite, and H

is sulfurous acid.

ClO is ammonium hypochlorate, and HClO is hypochlorous acid.

Polyatomic anions without oxygen have no odd endings to deal with. Sometimes they have prefixes, but

they’re a little more obscure, and you should get the formula with the name and vice versa. You just have

to know them.

There is only one common polyatomic cation, the ammonium ion, NH

. It just keeps its name as in the

formula above (ammonium hypochlorite).

It may be a big PIA, but you simply have to know these naming conventions. You will not be able to look

them up every time.

Naming Compounds And Determining Formulas Page 3

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