Naming Compounds That Contain Polyatomic Ions

Did you know that many common household substances, such as baking soda, are ionic compounds?

B5.5 Baking soda
Baking soda is a more complex ionic compound than the binary ionic compounds you just learned about. The IUPAC name of baking soda is sodium hydrogen carbonate and the chemical formula is NaHCO3. Ionic compounds that contain more than two elements will contain a polyatomic ion. A polyatomic ion is a group of elements that act as unit and have a charge. The majority of these ions are anions; however, there is one cation polyatomic that you will be working with in this course: ammonium, «math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«msup»«mi»NH«/mi»«mrow»«mn»4«/mn»«mo»+«/mo»«/mrow»«/msup»«/math». In your Science 10 data booklet, there is a table that identifies the common polyatomic ions. Compounds that contain polyatomic ions are classified as ionic compounds and, as such, have similar rules for naming and writing formulas.

  Watch This

Formulae of Ionic Compounds and Their Names: Part 2 @ YouTube FuseSchool – Global Education 


This video goes over some examples of writing formulas and naming compounds that contain polyatomic ions. Please note that in this video they use capital letters when writing names of compounds; this is not proper format. The last 40 s of this video goes on to give examples of multivalent ions. You will learn about multivalent ions later in the lesson.

Hint: If the compound contains a metal, it is an ionic compound.



 


  Digging Deeper

Bleach has the IUPAC name of sodium hypochlorite and the formula NaClO. Many polyatomic ions contain oxygen. There is a pattern that relates the number of oxygen atoms to the polyatomic name. If the polyatomic ion ends with “–ate,” that is the “base” oxyanion name in the series. If there is a “per– “ prefix added, there is one more oxygen in the “base” oxyanion formula. If the suffix changes to “–ite,” there is one less oxygen atom in the formula. And if there is a “hypo–” prefix, there is even one fewer oxygen.
B5.6 Bleach

  Did You Know?

B5.7 Soap making

Strong bases, such as lye, which is used to make soap, are ionic compounds of hydroxide. This makes base formulas easy to recognize!

sodium hydroxide—NaOH
potassium hydroxide—KOH
lithium hydroxide—LiOH

  Naming Compounds That Contain Polyatomic Ions Cont'd


Regardless of the number of elements in the compound formula, the name will consist of two parts: the cation name and the anion name. If you find yourself stringing several element names together to name a compound name, chances are the compound contains a polyatomic and you need to look for the polyatomic name in the table.

Examples


Each example has a video to go with it. To play the video, click on the play icon next to the example.
Identify the composition of the compound.

K+—metal
«math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«msup»«msub»«mi»SO«/mi»«mn»4«/mn»«/msub»«mrow»«mn»2«/mn»«mo»-«/mo»«/mrow»«/msup»«/math»—polyatomic
This is an ionic compound.
Write the name of the cation.

potassium
Write the name of the anion (if it is a polyatomic, do not change the ending; if it is a non-metallic element, change the ending to “ide”).

Combine the ion names.

potassium sulfate

Watch this video to see a teacher work through this example.  https://adlc.wistia.com/medias/z5h9i9btsv
 

Identify the composition of the compound.

Li+—metal
«math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«msubsup»«mi»NO«/mi»«mn»2«/mn»«mo»-«/mo»«/msubsup»«/math»—polyatomic
This is an ionic compound.
Write the name of the cation.

Write the name of the anion (if it is a polyatomic, do not change the ending; if it is a non-metallic element, change the ending to “ide”).

Combine the ion names.

lithium nitrite

Watch this video to see a teacher work through this example.  https://adlc.wistia.com/medias/hw837oanwo
 


Identify the composition of the compound.

«math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«msubsup»«mi»NH«/mi»«mn»4«/mn»«mo»+«/mo»«/msubsup»«/math»—polyatomic
Cl–—non-metal
This is an ionic compound.
Write the name of the cation.

ammonium
Write the name of the anion (if it is a polyatomic, do not change the ending; if it is a non-metallic element, change the ending to “ide”).

Since Cl is chlorine, a non-metal, the element name changes to end in “ide.”
Combine the ion names.

ammonium chloride

Watch this video to see a teacher work through this example.  https://adlc.wistia.com/medias/jn0n07wj75
 


Identify the composition of the compound.

«math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«msup»«mi»Ca«/mi»«msup»«mn»2«/mn»«mo»+«/mo»«/msup»«/msup»«/math»—metal
H2PO4–—polyatomic
This is an ionic compound.
Write the name of the cation.

Write the name of the anion (if it is a polyatomic, do not change the ending; if it is a non-metallic element, change the ending to “ide”).

dihydrogen phosphate
Combine the ion names.

calcium dihydrogen phosphate

Watch this video to see a teacher work through this example.  https://adlc.wistia.com/medias/a8ht0ysqk5
 



  Read This

Please read pages 44 to 46 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on the rules for naming ionic compounds that contain polyatomic ions. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.

  1. Provide the correct IUPAC name for each of the following compounds.

    ZnCO3
    Li3PO4
    Ba(OH)2
    MgSO3
    NH4Br
    KMnO4
    NaHSO4

    ZnCO3
    		 zinc carbonate
    Li3PO4 lithium phosphate
    Ba(OH)2 barium hydroxide
    MgSO3 magnesium sulfite
    NH4Br ammonium bromide
    KMnO4 potassium permanganate
    NaHSO4 sodium hydrogen sulfate