If you’re a chemistry teacher, you have probably experienced teaching your heart out– just working away teaching nomenclature. They’ve got it! Great! Then, the first assignment comes along, and students promptly begin sticking roman numerals and prefixes everywhere! Ugh! What are they thinking? What is the best way to teach this concept in a way that matches how the students are thinking?
-students promptly began sticking roman numerals and prefixes everywhere! Ugh!
It is difficult to view a chemical formula through the eyes of an average student. But, I’m willing to bet that they don’t see what we think they see. They see letters (some upper case, some lower case) and numbers (some normal sized, some subscript, and some superscript). It’s a jumbled mess. Through the years, I have tried several different approaches to teaching nomenclature, and I want to share with you the method I’ve been using for the past several years, that has turned out to be very successful. It’s not really a method- it’s more of a methodical step-by-step approach, utilizing and building on prior knowledge with each step. This is just the basic outline. Be sure to add activities, task cards, partner work, or group work along the way to reinforce the lessons.
Access Prior Knowledge:
Students must have a good understanding of bonding before moving into nomenclature. They need to understand the difference between ionic and covalent bonding, and within this context have a general understanding of polyatomic ions. Also, before moving forward, they should be able to identify whether an element is a metal or nonmetal by looking at the periodic table. And finally, an understanding of the basic concept of why atoms bond in the first place really helps students understand compounds. Why don’t atoms just move around on their own? Because unless it is a group 18 noble gas, atoms are very unstable. They bond to decrease potential energy, and increase stability. Therefore, compounds are stable, neutral units–either ionically or covalently bonded. For ionic compounds this means that the net effect of the ion charges must equal zero.
Order of Instruction:
We begin by sorting through the jumble of letters and numbers, and this is done through vocabulary. You could start this portion with an inquiry activity-sorting and coming up with their own definitions. Review the vocabulary words monatomic and polyatomic ions, and give students a list of polyatomic ions. Then, break ionic compounds down into binary and ternary compounds. Yes, use the word “ternary”. This will be a new vocabulary word for most students which will cause the brain to signal new learning. We want them to identify the word ternary with polyatomic ion present.
1. Ionic Compound Nomenclature (No multivalent cations yet!)
Begin ionic compounds by teaching ion formation for the different groups, i.e. group 1 will form +1 ions, etc. This is major! Discuss valence electrons and ions formed. Have students write the ions formed above each group 1,2, 3-18 on their periodic table. Remember, we’re leaving multivalent alone for now. We also want students to notice (or discover) that metals form cations, and nonmetals form anions. Then, begin by demonstrating that the net effect of the ionic charges must equal zero.
After a few demonstrations, show students the “cross-over” method. They will love you for this short cut. I always tell them that this works 98% of the time. (The only time that it doesn’t work is when they have to reduce the subscripts.)
Next, teach naming ionic compounds (still without the multivalent cations). Guide students to notice that if the compounds is ternary there is a polyatomic ion present. This also helps with that trouble maker ammonium, and something like cyanide. If they see more than two elements–boom!–ternary-use polyatomic ion sheet. Then you’ll just need to teach binary naming–replace the ending of the anion with -ide. Let students practice and get comfortable with binary and ternary ionic compounds.
2. Ionic Compound Nomenclature for Compounds with Multivalent Cations
Write “iron oxide” on the board. Explain that iron has two different oxidation states
(Fe+2 and Fe+3). So, which iron is it? There’s no way of telling, so we must add into the name which iron it is. Introduce roman numerals.
First, have students write formulas from names. This is fairly easy, but it seems that we have to say over and over that the roman numeral indicates the charge of the metal!! Keep saying it, asking it, over and over, until they’re rolling their eyes, huffing, and breaking into uncontrolled laughter.
Then comes the fun part–teaching writing names from formulas. The big deal concept here is that we want students looking at that cation first!! We get kind of a chant going: Is it metal or ammonia? YES. Is it a transition metal or p-block metal? YES. What must we do? “Check to see if it has more than one charge. Students will need a list of multivalent monatomic ions on the back of the polyatomic ion list. Also, list the transition elements with only one charge: zinc, silver, cadmium, tungsten. (To Get Your Free Ion Table Click Here) I know there are periodic tables with charges on them, but keep it simple for now with a list. I don’t give them a periodic table with charges until we study oxidation numbers. Student question: “Is it wrong if we put a roman numeral and the metal just has one charge?” Answer: Yes. We don’t write zinc (II) chloride. That would imply that zinc has more than one charge.
Practice throughout the lessons: “Is it ionic?” Response: “Yes!” “How do we know?” Response: “Metal to Nonmetal!” “Or?” Response: “Ternary!”
3. Acids & Hydrates
I have found that teaching acids and hydrates is a breeze. They get it! And, I like to teach both of these with ionic nomenclature. Treat it like interpreting a code.
First concept: All acids begin with hydrogen (H+1). “Is it an acid?” Response: “Yes!” “How do we know?” Response: “Begins with hydrogen!”
Next: I know there are all kinds of cute mnemonics out there for converting polyatomic ion names to acid names. Sometimes I feel these make things more complicated than necessary. I just keep it simple: “-ate to -ic & -ite to -ous!”
Finally, we write acid formulas using the cross-over method for ionic compounds. “Is it and acid?” Response: “Yes!” “How do we know?” Response: “It has the word acid!”
The biggest thing about naming and writing formulas for hydrates is to say over and over that it is the only ionic type of compound that we get to use prefixes!!! And, the prefixes are used only to tell how many water molecules are attached to the ionic crystal.
4. Molecular Formulas
I always start out by making a big deal that we have finally arrived at the moment they have all been waiting for: using prefixes! And, I tell them that this is so easy you just won’t believe it! First, they will always be binary! (For the scope of this course) That’s easy. They will always end in -ide. And, the prefixes tell us exactly how many atoms of each element are present! How easy is that.
Then there are just some small housekeeping details, such as not using mono on the first element, or not naming CO carbon monooxide, but carbon monoxide.
As you move along with the lessons, keep adding previously learned nomenclature to their assignments! This is important! Don’t work on each thing separately, and then mix it all up at the end. They will be totally overwhelmed. So, beginning with Ionic (II), we’ll call it, (adding multivalent cations), have them work some for practice, and then end with a section that has both Ionic (I) and Ionic (II) mixed together. After acids and hydrates, have them practice the new learning, and then mix it up at the end (mix with ionic compounds from above). And finally, after practicing molecular, have a section on the same page where they are all included and mixed up.
For review before a quiz or test on nomenclature, try some review activity where students are working separately, but together. What I mean by this is, students are working on their own work, but have a partner or group that can assist near by. Also, this is a time to monitor individual students needing extra help. I like task cards, naming races, naming tag races, white board work, Scoot, etc. One of my favorite is using task cards. There are many ways to use task cards, but one of my favorites is with white boards. I have a class set of large (48″ x 48″) white boards. When each student has one, it’s like having wall to wall white board, and it’s very easy to monitor.
I hope this helps with your teaching of nomenclature.
Until next time…