Chapter 3 Section 3.5 Guideline #3 Tasks #5 & #6 Study Guide
                  Polyatomic Ions

 Polyatomic Ions are explained in Chapter 3 Section 3.5 Guideline #3.


1.      When two or more elements, both nonmetals /or a transitional metal and a nonmetal, are attached by covalent bonds the group is either a molecule or a polyatomic ion. These bonds may be single, double, or even triple covalent (explained in Chapter 6)


2.      If the two bonded elements have no charge, then we have made a molecule (Tasks 3 & 4)


3.      However, if these two or more elements bonded together have a net ionic charge, then this group of atoms is a called a Polyatomic Ion and it is only one half of a compound.


4.      If the polyion has a positive charge, it is called a CATION. The most common positive polyatomic ion is Ammonium  NH41+. (There are less than 10 polyatomic cations)


5.      If the polyatomic ion has a negative charge, it is called an ANION.  An example of a negative polyatomic ion is Nitrate  NO31-. (There are over 130 polyatomic anions)


6.      If you put the two ions together in a one to one ratio you have the ternary ionic compound: Ammonium Nitrate NH4NO3.*


      *( The chemical compound ammonium nitrate, the nitrate salt of ammonium, has the chemical formula NH4NO3, simplified to N2H4O3. It is a white crystalline solid and is highly soluble in water. It is predominantly used in agriculture as a high-nitrogen fertilizer. The compound is used as an explosive in mining, and also sometimes in improvised explosive devices. It is the main component of ANFO, a popular explosive, which accounts for 80% of explosives used in North America. It is used in some instant cold packs, as hydrating the salt is an endothermic process.)


7.      Posted on our web site is a table which has about 99% of all polyatomic ions known and used in compounds in chemistry. The link to this complete list of over 140 ions is:


8.      Beginning chemistry books (CHM 1025C) always have a list of “common” polyatomic ions in their chapter on Nomenclature. Hein’s 14th  Table list 17 ions:

Corwin’s 6th Table list 19 ions:


9.      It is important for Premed, Science and Engineering majors chemistry sequential classes that students must know the names, the formulas, and charges of a longer list of polyions with at least 25-30 common polyatomic ions. The chemistry CHM 2045C/CHM 2046C textbook: Jespersen 7th is the current FSCJ major text has 27 common ions:

Other textbook tables:
Polyatomic Ion Charts from Selected Textbooks
Table 3.2    Corwin: Table 7.03
Table 2.5     Tillery: Table 9.3
Table 3.1      Hill:     Table 5.04


10.  Your instructor has examined how the textbooks and faculty peers in high school, introductory and general college chemistry courses approach teaching the names and formulas of polyatomic ions. A survey of over 50 texts at the three levels show all textbooks introduce polyatomic ions, some devote a separate section in the compound chapter, while others may have only one paragraph, but all have a listing of common polyatomic ions in a table. Chemistry faculty do not have a consensus on how to teach this subject. Most Chemistry faculty address the subject in three ways:

a.       Some give the students a list (or the table in the textbook) and require them to memorize the formulas and the charges.

b.        Then others provide the students with a list, but allow the students to use the list on exercises and tests.

c.        Some only allow the students to use the list on the first test, and expect the students to learn through rote usage the formulas and charges, but do not allow the list on future tests. 

P.S. Also, some faculty provide a crutch by allowing the students to write notes, problem solving formulas, and also polyatomic ions on a single piece (Crib Sheet) of paper to use during a test.

A search of Google reflects 426,000 hits for polyatomic ions. Most are static lists/tables. Many web sites go the next step to draw the Lewis Dot Structure of polyatomic ions, but with this many hits the Polyatomic Ions are very important in chemistry. (The first image in the goggle list is the long required (55-65) list I posted on the Internet,)


So how do we teach Polyatomic Ions?


11. In my 1025C, 2045C, and 2046C classes I give them list from the current textbook. I ask them to memorize the list including names, formulas, and charges. The next class period they take a test on this list. This is step 1 that I use in these three classes, mainly for the student to understand that having these Names, Formulas, and Charges at their fingertips for the next year is a difficult task. Ok, many take a test just to pass, then a week later they have buried the links in their brain to the formulas and charges and write nitrate’s charge as -2 instead of  -1 and the put four oxygen atoms in the formula instead of three.


 Most make 100% after one night, but some have a lot of trouble. They mix up the formulas and the charges. This was me many-many years ago in my first chemistry class, except I had a list 50 and one night to memorize them



12. In Step #2, the student turns in her/his common polyatomic ion test and I them give them a new list of 65 ions:

and I tell them they will take one of three tests on these ions the next class period, followed by two un-announced Progressive Polyion tests before the end of the course. I created an online flash card version for the student to practice:


13. So here is the student’s problem:

The Polyatomic Ion Problem!

Knowing dot structures (Using only the Octet Rule) of polyatomic ions (Suchocki’s Chapter 6), and some keen observations you can boil it down to six questions to determine the formula and the charge on a polyatomic ion :

1.   What is the formula for the –ate polyatomic ion?

2.   What is the charge on –ate polyatomic ion?

3.   What happens when you attach hydrogen atom(s) to the polyatomic 2- and 3- anions?

4.  What does ite mean in a polyatomic ion?

5.   How do the hypo- and per- prefixes apply to polyatomic ions?

6.   What are the two ide polyatomic negative charged Anions and the two -ium positive charged polyatomic Cations?


14. Here is my solution to the problem created for them. I teach two algorithms that if they learn, then at anytime they can look at a periodic chart and figure out the Polyion’s formula and charge, but before they learn to use these algorithms they must have studied bonding (Chapter 6).

     Read the following, if you want to try to see the solution:


  1. Answer the Above Questions
  2. Taylor's -ate 3/4 Oxygen Rule
  3. Taylor's -ate Charge Rule
  4. This method was published in the Fall of 2014 in the 2YC3 newsletter and you can read it:




Page 9, the published article:



15.  Our author, John Suchocki, does not spend much time with Polyatomic ions in Section 3.5. He has the smallest common ion table of (3.1) any chemistry textbook with only 9 ions:




So what do we do in  this  CHM 1020 class?


Suchock’s table does not have enough ions. This is CHM 1020, so you do not have to memorize any of the ions, just know how to use them in writing chemical formulas of ternary ionic compounds and also ternary acid compounds.


 You should always have the list of 55:

available when you are writing chemical formulas.



(In my CHM 1032C for allied health chemistry, I do likewise and provide the list on the backside of a periodic table. So our nursing majors taking 1020 instead of 1032C you do not need to have these at your finger tips too.)






          Look at the list of polyatomic ions below we will use when we
          write the Names or Formulas of make Ternary Ionic Compounds:          
     -ate Polyatomic ions with four oxygen atoms
     -ate Polyatomic ions with three oxygen atoms
     Polyatomic ions which also contain hydrogen
     -ide Polyatomic ions (and also Cyanate which is different)
     Positive Charged (Cation) Polyatomic Ions


      Discover Polyatomic Ion Formula and Charges from Interactive Web Page:
      Click image below to hyperlink to this site: