Lesson 5 Ionic Compounds - Naming and Formulas
Writing Formulas for Compounds that contain Multivalent Ions
How do we deal with particular metals that have multiple ion charges?
© Wikimedia Commons
B5.9 Chromium(VI) oxide
B5.9 Chromium(VI) oxide
The movie Erin Brockovich is based on a real court case in which a company caused hexavalent chromium to leach into water supplies, resulting in devastating health effects of the residents of Hinkley, California. Hexavalent chromium is toxic,
corrosive, and carcinogenic. But what does hexavalent mean?
Some metals can form ions with various ion charges; for example, chromium can have ion charges of «math»«msup»«mi»Cr«/mi»«msup»«mn»6«/mn»«mo»+«/mo»«/msup»«/msup»«mo»,«/mo»«mo»§#160;«/mo»«msup»«mi»Cr«/mi»«msup»«mn»3«/mn»«mo»+«/mo»«/msup»«/msup»«mo»,«/mo»«mo»§#160;«/mo»«mi»and«/mi»«mo»§#160;«/mo»«msup»«mi»Cr«/mi»«msup»«mn»2«/mn»«mo»+«/mo»«/msup»«/msup»«/math» and more rarely «math»«msup»«mi»Cr«/mi»«mo»+«/mo»«/msup»«mo»,«/mo»«mo»§#160;«/mo»«msup»«mi»Cr«/mi»«msup»«mn»4«/mn»«mo»+«/mo»«/msup»«/msup»«mo»,«/mo»«mo»§#160;«/mo»«mi»and«/mi»«mo»§#160;«/mo»«msup»«mi»Cr«/mi»«msup»«mrow»«/mrow»«mrow»«mn»5«/mn»«mo»+«/mo»«/mrow»«/msup»«/msup»«/math». Unlike hexavalent chromium, most other chromium ion compounds are not dangerous. The compound name that contains a multivalent metal must clearly identify which valiancy is in the compound. This is achieved by the use of Roman numerals.
The steps for writing formulas for multivalent ionic compounds are essentially the same as they are for binary ionic compounds. The one difference is that you can determine the cation charge without checking the periodic table. The given Roman numeral following the metal ion is equal to the magnitude of the positive charge on the ion.
Some metals can form ions with various ion charges; for example, chromium can have ion charges of «math»«msup»«mi»Cr«/mi»«msup»«mn»6«/mn»«mo»+«/mo»«/msup»«/msup»«mo»,«/mo»«mo»§#160;«/mo»«msup»«mi»Cr«/mi»«msup»«mn»3«/mn»«mo»+«/mo»«/msup»«/msup»«mo»,«/mo»«mo»§#160;«/mo»«mi»and«/mi»«mo»§#160;«/mo»«msup»«mi»Cr«/mi»«msup»«mn»2«/mn»«mo»+«/mo»«/msup»«/msup»«/math» and more rarely «math»«msup»«mi»Cr«/mi»«mo»+«/mo»«/msup»«mo»,«/mo»«mo»§#160;«/mo»«msup»«mi»Cr«/mi»«msup»«mn»4«/mn»«mo»+«/mo»«/msup»«/msup»«mo»,«/mo»«mo»§#160;«/mo»«mi»and«/mi»«mo»§#160;«/mo»«msup»«mi»Cr«/mi»«msup»«mrow»«/mrow»«mrow»«mn»5«/mn»«mo»+«/mo»«/mrow»«/msup»«/msup»«/math». Unlike hexavalent chromium, most other chromium ion compounds are not dangerous. The compound name that contains a multivalent metal must clearly identify which valiancy is in the compound. This is achieved by the use of Roman numerals.
If no indication is given (i.e., no Roman numerals), then assume the most common ion charge is present, which is the one written first on the periodic table.
The steps for writing formulas for multivalent ionic compounds are essentially the same as they are for binary ionic compounds. The one difference is that you can determine the cation charge without checking the periodic table. The given Roman numeral following the metal ion is equal to the magnitude of the positive charge on the ion.
© Wikimedia Commons
B5.10 Chromium(III) oxide
B5.10 Chromium(III) oxide
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 type of compound.
chromium—metal
fluoride—non-metal
This is an ionic compound.
fluoride—non-metal
This is an ionic compound.
Write the ion symbols.
«math»«msup»«mi»Cr«/mi»«msup»«mn»3«/mn»«mo»+«/mo»«/msup»«/msup»«mo»§#160;«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«msup»«mi mathvariant=¨normal¨»F«/mi»«mo»§#8211;«/mo»«/msup»«/math»
Determine the lowest common multiple of the two charges.
The lowest common multiple between 3 and 1 is 3.
Determine the factor to multiple each ion by.
«math»«mtable columnspacing=¨0px¨ columnalign=¨right center left¨»«mtr»«mtd»«msup»«mi»Cr«/mi»«msup»«mn»3«/mn»«mo»+«/mo»«/msup»«/msup»«mo»§#160;«/mo»«mo»§#215;«/mo»«mo»§#160;«/mo»«mn»1«/mn»«mo»§#160;«/mo»«/mtd»«mtd»«mo»=«/mo»«/mtd»«mtd»«mo»§#160;«/mo»«mn»3«/mn»«mo»+«/mo»«/mtd»«/mtr»«mtr»«mtd»«msup»«mi mathvariant=¨normal¨»F«/mi»«mo»§#8211;«/mo»«/msup»«mo»§#160;«/mo»«mo»§#215;«/mo»«mo»§#160;«/mo»«mn»3«/mn»«mo»§#160;«/mo»«/mtd»«mtd»«mo»=«/mo»«/mtd»«mtd»«mo»§#160;«/mo»«mn»3«/mn»«mo»§#8211;«/mo»«/mtd»«/mtr»«/mtable»«/math»
This will create a neutral compound.
The ratio of «math»«msup»«mi»Cr«/mi»«msup»«mn»3«/mn»«mo»+«/mo»«/msup»«/msup»«/math» to F– is 1:3.
This will create a neutral compound.
The ratio of «math»«msup»«mi»Cr«/mi»«msup»«mn»3«/mn»«mo»+«/mo»«/msup»«/msup»«/math» to F– is 1:3.
Watch this video to see a teacher work through this example. https://adlc.wistia.com/medias/0cj3jt7ano
Identify the type of compound.
copper—metal
sulfate—polyatomic
This is an ionic compound.
sulfate—polyatomic
This is an ionic compound.
Write the ion symbols.
«math»«msup»«mi»Cu«/mi»«msup»«mn»2«/mn»«mo»+«/mo»«/msup»«/msup»«mo»§#160;«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«msubsup»«mi»SO«/mi»«mn»4«/mn»«mrow»«mn»2«/mn»«mo»-«/mo»«/mrow»«/msubsup»«/math»
These subscripts can be reduced to CuSO4.
These subscripts can be reduced to CuSO4.
Determine the lowest common multiple of the two charges.
The lowest common multiple between 2 and 2 is 2.
Determine the factor to multiple each ion by.
«math»«mtable columnspacing=¨0px¨ columnalign=¨right center left¨»«mtr»«mtd»«msup»«mi»Cu«/mi»«msup»«mn»2«/mn»«mo»+«/mo»«/msup»«/msup»«mo»§#160;«/mo»«mo»§#215;«/mo»«mo»§#160;«/mo»«mn»1«/mn»«/mtd»«mtd»«mo»=«/mo»«/mtd»«mtd»«mo»§#160;«/mo»«mn»2«/mn»«mo»+«/mo»«/mtd»«/mtr»«mtr»«mtd»«msubsup»«mi»SO«/mi»«mn»4«/mn»«mrow»«mn»2«/mn»«mo»-«/mo»«/mrow»«/msubsup»«mo»§#160;«/mo»«mo»§#215;«/mo»«mo»§#160;«/mo»«mn»1«/mn»«mo»§#160;«/mo»«/mtd»«mtd»«mo»=«/mo»«/mtd»«mtd»«mo»§#160;«/mo»«mn»2«/mn»«mo»§#8211;«/mo»«/mtd»«/mtr»«/mtable»«/math»
This will create a neutral compound.
The ratio of «math»«msup»«mi»Cu«/mi»«msup»«mn»2«/mn»«mo»+«/mo»«/msup»«/msup»«mo»§#160;«/mo»«mi»to«/mi»«mo»§#160;«/mo»«msubsup»«mi»SO«/mi»«mn»4«/mn»«mrow»«mn»2«/mn»«mo»-«/mo»«/mrow»«/msubsup»«/math» is 1:1.
This will create a neutral compound.
The ratio of «math»«msup»«mi»Cu«/mi»«msup»«mn»2«/mn»«mo»+«/mo»«/msup»«/msup»«mo»§#160;«/mo»«mi»to«/mi»«mo»§#160;«/mo»«msubsup»«mi»SO«/mi»«mn»4«/mn»«mrow»«mn»2«/mn»«mo»-«/mo»«/mrow»«/msubsup»«/math» is 1:1.
Watch this video to see a teacher work through this example. https://adlc.wistia.com/medias/vize8c3fee
Read This
Please read page 44 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on determining the cation’s charge from
the Roman numerals. 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.- Provide the correct IUPAC name for each of the following compounds.
iron(III) sulfate gold(I) sulfide nickel(II) nitrite manganese(IV) oxide
iron(III) sulfate Fe2(SO4)3 gold(I) sulfide Au2S nickel(II) nitrite Ni(NO2)2 manganese(IV) oxide MnO2