descriptive chemistry of the elements

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Adam R. Johnson, Harvey Mudd College
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descriptive chemistry of the elements

I think we can all agree that the descriptive chemistry of the elements (I am thinking mostly of the p block, but some aspects of the d block as well) is:

  • important
  • hard or boring to teach

This may be a generational thing, and maybe I'm young(er), and the pendulum is way on one side, but when I read books like Cotton & Wilkinson or Greenwood & Earnshaw, where they say that facts are more important than theories, I tend to disagree.  Some of my coworkers, however, firmly believe that facts trump theories.  Given the limited time we all have to teach inorganic chemistry, one has to make choices about content to include or discard.  I have tended to spend a lot (my students might say a LOT) of time on MO theory, while paying only the barest lip service to descriptive chemistry.  I have, once or twice, taught units on halogens and noble gas chemistry (since those are at least things the students have not seen, especially noble gas chemistry), but these days, I have added units on the "more important" fields of organometallics or solid state or bioinorganic.  I put a little descriptive chemistry in here and there, where it fits (VSEPR is a good place to at least mention a little, for example, why you can form IF7 but only ClF5 or BrF5) and I put quite a bit in my acid/base unit (that I teach in Analytical).

 

Any thoughts from the collected masses on this topic?  I don't really have a question (or a point, perhaps) but I am curious how others think about this topic.

Adam 

 

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Nancy Scott Burke Williams, Scripps College, Pitzer College, Claremont McKenna College
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I find that my course is very similar in the topics covered, and I often give such descriptive chemistry short shrift as a separate topic in my course, but I end up flavoring everything with a little fact here, a little fact there, and I often talk about descriptive trends on their own. 

Alas, I must side with your colleagues. Facts trump theory. Adherence to theory in the face of contrary facts is a far more unforgivable scientific sin that adherents to facts in the face of a contrary theory. As John Maynard Keynes said (allegedly) when accused of having just said something which contradicted an earlier pronouncement of his, "When the facts change, I change my opinions. What do you do, sir?"

But I think what you're getting at is that it makes more sense to teach theory, and I think that's sound. Not because theory is superior, but because it's more succinct. You can much more easily grasp the wide body of information in inorganic chemistry if you place it into a theoretical framework-even a wrong one. Theories provide the scaffolding for the facts, which are the bricks.

When the scaffolding can no longer support the facts, you get new scaffolding, but only an idiot tries to build a tall building with bricks alone. That's why I tend to teach "scaffolding first" even though the whole point of the endeavor is to make a brick building.

Add to that the sheer number of facts relative to central theoretical concepts, and you see how much more reasonable is seems to not follow a "bricks first" approach to teaching inorganic. After all, we only have one semester.

Meghan Knapp, Georgetown College
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I much prefer to have a theoretical basis for facts than to simply memorize the facts.  Unfortunately there are times when a sufficient theory doesn't exist that adequately explains all the facts.  I struggle with how to present this material to my students.

I have just begun to teach a course titled "Descriptive Inorganic Chemistry".  I have taught it two semesters, with different texts and content each time, and plan to change again the next time I teach it.  The course is to be accessible to students who have successfully completed freshman chemistry.  I just have a hard time deciding which are the important pieces and which are minutia.  I mostly deal with transition metals and with the Advanced Inorganic Chemistry these tend to be the focus, so I really want to focus of DIC to be on the descriptive chemistry of the main group elements.   Are there important overarching theories in Main Group Chemistry that I should be sure not to miss?  What are the "facts" that my students should know, even if there is not a good theory to explain them?  With so much content, what should I cover in a semester?  Is this content best taught by groups on the table, or by contexts such as electro-chemistry, acid/base chemistry, etc?

Barbara Reisner, James Madison University
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I've never had to teach a group on descriptive inorganic chemistry, nor do I teach much.  (For that matter, this topic wasn't covered in either my undergraduate or graduate coursework.)  I like the idea of having a theoretical underpining to everything I teach since students seem more able to make sense rather than memorize.  One book that seemed to do this was  D. M. P. Mingos Essential Trends in Inorganic Chemistry.  Check out the textbook reviews for more info - Maggie has written a review of this book.
Barbara Reisner, James Madison University
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Although it's not what I would traditionally classify as descriptive chemistry, I'm having a lot of fun listening to short (< 10 minutes) podcasts put out by the Royal Society's Magazine Chemistry World called Chemistry in its Element.  While they don't provide a comprehensive description of each element, they all have a sense of fun.  They remind me a lot of John Emsley's books.  (He does the pdocast on Magnesium.)  I think this could be a fun way to introduce lighter aspects of descriptive chemistry to students.
Daniel Southam, Curtin University of Technology
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I  have the same problem of how to approach teaching my half of a 2nd year unit of what could be called descriptive main group chemistry.  What makes this particular unit difficult is it lacks a laboratory component, and other more engaging descriptive topics (d-block particularly) are covered in subsequent units.  The students often feel it doesn't fit well with their expectations of what chemistry "is"!

Our inorganic/analytical chemistry teaching group all tend to resort to the Oxford Chemistry Primers when we're stumped by how to start with a topic, and I've found the Main Group one to be particularly useful here.  They lack teaching resources entirely, but the students love them.  They're on reserve in our library and during semester you can't get a copy!  My colleague who teaches Organometallics in the following semester swears by the two relevant volumes.

We currently use Miessler & Tarr as the main 2nd/3rd year text, which the students then feel able to tackle.  They also tend to use Greenwood & Earnshaw and Advanced Cotton & Wilkinson when wanting to zero in on a particular element.

Cheers,

Daniel

PS: Thanks to Joanne Stewart who presented at yesterday's session of the Royal Australian Chemical Institute's Chemical Education Division conference and introduced us to VIPEr.  While the Australian university system is a little different to the US, hopefully I can contribute some ideas along the way and take some ideas presented into my lectures and labs!

Joanne Stewart, Hope College
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Welcome to VIPEr, Daniel!

I've had fun putting some of the descriptive main group chemistry back in the hands of the students. I let them choose an application of a main group element to research. In order to get broad coverage, I think I assigned them a group from the Periodic Table, but let them pick the element and the application. The last time I did this, we didn't have cool things like wikis, so they just did a paper and a presentation. If I do it again, I'll probably have them create some sort of a class wiki. I think someone on the IONiC leadership council (Maggie?) did this last year.

I have to say, the students were more engaged in this activity than I expected. Many of them were able to connect it to a job they've had or a hobby, and I think that personal connection made the difference. I've posted this as a learning activity in the Main Group section of VIPEr, but I just realized I haven't uploaded any of the handouts for it. I'll have to look for those.

Maggie Geselbracht, Reed College
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Yes, I experimented with a descriptive chemistry wiki assignment last spring and hope to improve it again this spring.  Here is the VIPEr link to the learning object I posted:

https://www.ionicviper.org/problem-set/create-descriptive-chemistry-wiki

Note that this learning object is classified as a Problem Set activity type, which means that you need to have Faculty status on VIPEr in order to access the materials.  If you cannot see it, and you are a graduate student, postdoc, or faculty member, you can request additional privileges on your account to gain access to this class of learning objects.

Randall Hicks, Wheaton College
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I'm guessing that many of us have seen (or at least heard of) the periodic table of videos put forth by University of Nottingham.

http://www.periodicvideos.com/

These videos are well done, informative and often humorous. Plus, I never get tired of Martyn Poliakoff's Einstein-esque hairdo! This could be another resource to breathe life into the corpse that is descriptive chemistry.

Charles Macdonald, University of Windsor
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The typical undergraduate progression in Canada is apparently different than the ACS-proscribed curriculum but I can at least tell you what I do for a 4th year (Senior) course in Main Group Chemistry.  I think that it is critical to provide the students with both the important theoretical constructs we use to understand the chemistry in addition to a variety of actual examples - especially if they highlight the flaws in the overly-simplistic models we tell them about at earlier stages in their education. 

I use the inexpensive primer called "Main Group Chemistry" by William Henderson (part of the Basic Concepts in Chemistry series by the RSC) as guide that the students won't mind purchasing.  The book covers many of the important theoretical models and enough descriptive chemistry of hydrides, oxides, halides, etc., and it includes problems and answers for the students to try.  I also suggest that they use Nick Norman's Oxford Chemistry Primer called "Periodicity and the s- and p-block Elements" if they want a somewhat more detailed description of some of the theoretical models involved.  The students will have learned about many of the simple models in Inorganic courses in their 2nd and 3rd years of their undergraduate programs.

Most of the additional material we examine comes from sources such as: A.G. Massey's "Main Group Chemistry, 2nd Ed."; parts of G. E. Rodgers' "Descriptive Inorganic, Coordination, and Solid-state Chemistry, 2nd Ed."; parts of G. Rayner-Canham and T. Overton's "Descriptive Inorganic Chemistry"; and even some parts of C. E. Housecroft and A. G. Sharpe's "Inorganic Chemistry, 3rd. Ed."; among others.  I also give them handouts from other sources about critical concepts such as the isolobal analogy, or the differences between valence states and oxidation states, etc.

Overall, my opinion is that no single book really covers all of the material in the manner I wish the students to understand it - and some books cling without caveat to incorrect but easy-to-teach models (e.g. d-orbital participation in the bonding of the p-block elements) - so I just have to put it together the way I want it.

Joanne Stewart, Hope College
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I'm struggling with the definition of descriptive chemistry, and this is important because I'm considering working with my Australian friends on a descriptive chemistry project, but I think they mean something very different by the term.

SO PLEASE HELP ME OUT HERE.

It seems like American inorganic chemists use the term descriptive chemistry to describe a survey of the elements, especially the main group elements. What are their oxidation states? What types of compounds do they form (with hydrogen, oxygen, nitrogen, etc.)? What types of reactions do they undergo?

The U.S. Advanced Placement community (high school students in the U.S. can take an advanced chemistry course and then take an AP test to receive college credit) seems to describe descriptive chemistry as the "facts" of chemistry, which they distinguish from "principles" and "concepts." Hmm. Not sure I know where those lines are drawn. (from http://www.collegeboard.com/student/testing/ap/chemistry/topic.html?chem...).

IV. Descriptive Chemistry (10-15%)

Knowledge of specific facts of chemistry is essential for an understanding of principles and concepts. These descriptive facts, including the chemistry involved in environmental and societal issues, should not be isolated from the principles being studied but should be taught throughout the course to illustrate and illuminate the principles. The following areas should be covered:

  1. Chemical reactivity and products of chemical reactions
  2. Relationships in the periodic table: horizontal, vertical, and diagonal with examples from alkali metals, alkaline earth metals, halogens, and the first series of transition elements
  3. Introduction to organic chemistry: hydrocarbons and functional groups (structure, nomenclature, chemical properties). Physical and chemical properties of simple organic compounds should also be included as exemplary material for the study of other areas such as bonding, equilibria involving weak acids, kinetics, colligative properties, and stoichiometric determinations of empirical and molecular formulas.

My Australian friends seem to mean mostly #2 in the list above when they say descriptive chemistry. It seems like they want their students to be able to "think chemistry," as in "What would you predict if.....?" But I'm pretty sure I don't really understand yet.

I would love to hear what others think, especially folks from outside the U.S. 

Adam R. Johnson, Harvey Mudd College
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I also did the descriptive chemistry wiki in spring 2009, and while the students did the research and posted on the wiki, in general, the student response to putting the wiki together  was poor. 

For this year I was thinking of assigning groups of students to various areas of the periodic table {s-block, p-block sections (ie, chalcogens, pnictogens, halogens, noble gases), 1st, 2nd, 3rd row d-block, Ln and Ac}.  Assuming I can count, thats 10 groups;  so I wouldn't use all of them in one year.  Then, each group would write a wiki page or paper describing chemistry, principles, etc.  Maybe tie in the inorganic nobel prizes too, where applicable. 

This is a work in progress, as I have 6 whole days to prep until spring 2010 starts...... so I will report back later with what I decided to do.  Especially if it worked well!

Adam

Adam R. Johnson, Harvey Mudd College
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by the way, Randall Hicks and I did create an inter-institutional writing project for teaching descriptive chemistry.  Here is the link:

https://www.ionicviper.org/problem-set/descriptive-inorganic-chemistry-w...

 

Nancy Scott Burke Williams, Scripps College, Pitzer College, Claremont McKenna College
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@ Joanne: Descriptive chemistry probably cannot be defined. It is the chemistry analog to "miscellaneous". Because the pKa trends of methane to HF falls under "acid-base chemistry", it is not descriptive.

In contrast, the greater tendency of the B-F series to form pi bonds than the lower p-block rows does not fall into our conceptual genchem textbook chapter scheme, and therefore it is descriptive. 

The best treatments I've seen use descriptive chemistry as an excuse to do a high level revisitation of "periodic trends". The worst are simple jumbles of miscellania. 

Almost by definition, once you think of a way to teach something that ties it to a larger idea in the course, it stops being descriptive chemistry. Perhaps that's my definition of descriptive chemistry after all. "Chemical knowledge I haven't figured out how to teach."