Diana Simpson

Posted about 2 years ago

I, too, teach the rules as we have learned them over the years. Many times my students will struggle with the ionic rules and then see the molecular rules as very easy, which is nice to have happen. Their understanding of the 'why' we do something is important and I have them see the differences in the two systems and the similarities. Then we go into Organic nomenclature and they truly understand why it is important to be as clear and specific as possible when naming any compound.

Kaleb Underwood

Posted over 2 years ago

Adrian - I absolutely agree! Wouldn't want to put students at a disadvantage. That being said, when I was at a public school in the state standards simply said "using IUPAC nomenclature rules." Not a very helpful guideline....

Adrian Dingle

Posted over 2 years ago

Kaleb - Thanks for referencing my blog post. Having said that, as I say in the post, I strongly advise following the 'local rules' when it comes to exams etc., i.e., don't challenge the authority of the exam!

Jennifer Bishoff

Posted over 2 years ago

I was always pretty strict about this in my Honors/AP class, but a little less so in my other classes. For classes that struggle, I had them create a flowchart to help them name, and sometimes even allowed them to use it on assessments. The top would say “Naming”, then split down into “Ionic” and “Covalent”. “Covalent” would describe how to determine if a compound is indeed covalent (nonmetal + nonmetal), then also include the prefixes used in this convention. “Ionic” would break into three sections: “Binary”, “Stock System”, and “Polyatomic” with descriptions and naming conventions of each. I think it’s easier to teach it as covalent has prefixes and ionic does not, because that helps them to keep it straight in their minds. Later, perhaps in college, they can learn to “relax” the rules.

Ryan Johnson

Posted over 2 years ago

I don't teach that, nor would I probably consider it. Neglecting prefixes in ionic compounds not only forces students to work in order to understand electrostatics and valence electron interaction, but I find that they're thrilled to have the "easier" covalent molecules to name after having put in all the effort with ionics first.

Kaleb Underwood

Posted over 2 years ago

It is not that prefixes on ionic compounds are “now accepted” but rather that the prefixes may be added when naming any inorganic compound. For example, calcium difluoride and calcium fluoride are both acceptable according to IUPAC. Generally, multiplicative prefixes are always permissible, but may be omitted when there is no possible ambiguity in the stoichiometry. This is likely where the “rule” that ionic compounds don’t get prefixes comes from.

As far as my class, I teach what would be called the “rules” found in introductory chemistry texts, but I also teach my students the purpose of nomenclature: the communication of the identity of chemical formulae without ambiguity as to their identity. I would accept calcium chloride, calcium dichloride, and calcium(II) chloride as names for CaCl2, but also expect students to produce the correct formula given only “calcium chloride.”

You will also see oxidation numbers used in molecular compounds, if the situation calls for it. For example, NO2 is nitrogen dioxide to most of us, but also may be named as nitrogen(IV) oxide.

I highly suggest reading Adrian Dingle’s excellent blog post on this matter. I came across it last year and was glad to see that he had put a name to the “non-ambiguity principle” I had previously used without a name and cited IUPAC support for it. https://www.adriandingleschemistrypages.com/nomenclature/why-you-should-stop-worrying-so-much-about-nomenclature/

As a side note, Adrian and I have been unable to identify the origin of the “rules” so many textbooks claim are written in stone. If anyone has any insight, please share.