Polyatomic Ions

Common Polyatomic Ions

Polyatomic Ions are compounds composed of different elements. All polyatomic ions have a positive or negative charge. 

Polyatomic Ions with Halogens

Concept: The 4 Characteristics of Polyatomic Ions with Halogens

Video Transcript

Remember the halogens are the elements in Group 7A. We're going to say that polyatomic ions that contain halogens are sometimes referred to as oxy halogens or halogen oxyanions. When we say oxy we mean that oxygen is present, so we're going to say that these polyatomic ions are going to have halogens and oxygen. And remember, when we say anions all we mean is a negative ion, so a negatively charged ion is called an anion.
Now we're going to say these compounds share four common characteristics. First thing, they contain one halogen. And remember, when we say halogen we mean Group 7A, so fluorine, chlorine, bromine or iodine. We don't worry ourselves with the last element in Group 7A, At, we're just focused on these four.
Next characteristic that they share is they contain one to four oxygens. So all these compounds are going to have halogens and they're going to have one to four oxygens.Next thing, they contain no other elements. And then finally, they possess a negative one charge. So that's the four characteristics all of these compounds in this video are going to possess.
Now we're going to say that these compounds use the same system for naming and it's all based on the number of oxygens that are present. 

Concept: Naming System for Polyatomic Ions with Halogens

Video Transcript

What we're going to say first is, for each non-metal, each non-metal has a base name. So fluorine is fluor-, chlorine is chlor-, bromine is brom-, and iodine is iod-, so those are the base names. Those base names are going to be positioned in each of these blanks here. That's what goes in each one of these blanks, the base name.
Now we're going to say based on the numbers of oxygens present, that's going to determine the name of our polyatomic ion.
So we're going to say when we have one oxygen present the prefix will be hypo, the beginning of the name will be hypo-. The beginning of the name will be hypo-. Based on the halogen present, it could have any one of these four base names. The ending, the suffix, will be -ite. So remember the prefix, which is the beginning of the name, will be hypo- and the suffix, which is the end of the name, will be -ite.
Now if we possess two oxygens, we drop the prefix hypo- but we keep the suffix -ite, and depending on which halogen you have you plug-in that base name. When we finally move on to three oxygens, the -ite that we have changes to -ate. And then finally when we get to four oxygens, we get a whole new prefix per-. We'll still we use one of these base names depending on which halogen is present, and then the ending will stay -ate. So just remember this pattern and you'll be able to answer any of these questions.

The naming system for polyatomic ions with halogens is based on the number of oxygens present. 

Polyatomic ions that contain only oyxgen and fluorine are imaginary and do not exist. However, in terms of naming we can still use the rules we learn to name these imaginary polyatomic ions. 

Example: Name each of the following compounds.

            a. BrO4 –                                                                                                          b.  FO2


            c. ClO –                                                                                     d.  IO3




Polyatomic Ions Additional Practice Problems

Bearing in mind the relationship between sulfate and sulfite or nitrate and nitrite, what is the formula of phosphite?

(A) PO43-

(B) HPO43-

(C) PO42-

(D) PO33-

(E) PO32-

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Which of the following has a charge of –1?

(A) ammonium

(B) carbonate

(C) phosphate

(D) sulfate

(E) acetate

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Which of the following does not have a charge of –1?

(A) nitrate

(B) hydroxide

(C) ammonium

(D) chloride

(E) acetate

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Recall that metals possessing multiple charges are referred to as Type II Metals. Below we have the formal or IUPAC name of some of the most common Type II metals as well as their older latin derived name. 

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Polyatomic ions are compounds made up of different elements that possess a CHARGE.


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The correct formula for bromite is:

A. BrO2-
B. BrO-
C. BrO3-
D. BrO5-
E. BrO4-

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The ion NO2 is named

A) nitrogen dioxide ion.

B) nitrogen(II) oxide ion.

C) nitrite ion.

D) nitrate ion. 

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Breaking News: At 11 am this morning NASA announced that they have evidence liquid water still flows on Mars. Water can stay liquid at such low temperature because of the high concentration of salt dissolved in the water, and some scientists believe perchlorate ions play a major role.


Write a formula for the perchlorate ion.

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The chemical name of the ion IO3- is:

a) periodate

b) hypoiodite

c) iodate

d) iodide

e) iodite

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The chemical name of the ion IO3 is:

a. periodate

b. hypoiodite

c. iodate

d. iodide

e. iodite

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The ion MnO4 is called permanganate, which would you expect the formula of the manganate ion to be?

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