Extended structure

25 Jun 2013

The Synthesis and Characterization of Cobalt Spinels

Submitted by Rebecca Ricciardo, The Ohio State University
Evaluation Methods: 

Students complete pre- and post-lab questions; these are within the document. Upon completion of the lab, the student is to write a lab report. A lab report is written in a format similar to that of a paper submitted for publication. Sections include the title & authors, abstract, introduction, experimental, results, discussion, conclusion and references.

Evaluation Results: 

The average score for the prelab assignements was 65% with a high of 100% and a low of 35%. The average score for lab reports was 92% with a high of 100% and a low of 71%. 

Students were able to index the patterns using the supplement (attached) as a guide. 

Description: 

In this lab, students will use solid-state methods to synthesize cobalt and chromium spinels, ZnCr2O4, ZnCo2O4, CoAl2O4, and CoCr2O4. They will (1) characterize their structure with X-ray powder diffraction (XRD) and (2) characterize the color using UV-Vis diffuse reflectance spectroscopy.

Corequisites: 
Prerequisites: 
Learning Goals: 

Upon completing this lab, students will:

  • Know how to synthesize polycrystalline materials using solid state synthesis techniques.
  • Gain experience preparing solid samples for diffraction analysis and collecting XRD data.
  • Be able to index XRD patterns from cubic materials to determine unit cell parameters.
  • Relate reflectance spectra to the visible colors of materials.

 

Equipment needs: 

Analytical balances

Mortars and pestles (agate or porcelain)

Crucibles (alumina or porcelain)

High temperature furnace (1000˚C)

Powder X-ray diffractometer

UV-Vis spectrometer equipped to do diffuse reflectance

Implementation Notes: 

This lab is the first lab in an upper level inorganic laboratory course. It is completed first, because the students must weigh out reagents and grind them in a mortar and pestle and then heat them for 8 hours at 1000˚C. The synthesis does not take a full lab period, which allows time for the first-day housekeeping items to be distributed and discussed. During the second lab period, student samples are returned and the students collect their XRD data and UV-Vis data. There is enough time for students to begin working through the analysis in class.

Note: This lab lends itself to many adaptations.

  • If there is no XRD access readily available for students, patterns may be provided so that students can index these, even if they have not collected the data.
  • The electronic transitions of these compounds may be analyzed with more detail (ie. assigning transitions).
  • Magnetic measurements may be made and the number of unpaired electrons deduced (this is Exp 3 that is referred to in the attached lab document).

 

Time Required: 
Sample must be heated for 8-10 hours, so the synthesis and characterization must be completed at two separate times: (1) 1-hour period for synthesis of compounds and (2) a 3-hour lab period for analysis.
25 Jun 2013

I created this Collection of Learning Objects (LOs) at the IONiC VIPEr TUES 2013 Workshop: Solid State Materials for Alternative Energy Needs held at Penn State University.  The overall theme of the Collection is electronic and optical properties of metals, semiconductors, and insulators.  Most of the learning objects either require knowledge of or explicitly refer to band structures, either at a basic level or a more advanced level.  Some LOs also deal with extended structures, un

Prerequisites: 
Corequisites: 
24 Jun 2013
Evaluation Methods: 

Student performance on Preliminary Questions (PQs) and reports are assessed

Percent yield and percent purity from UV-Vis and titration analyses

Accuracy in completion of table of IR bands/assignments

Answers to Thought Questions

Evaluation Results: 

Percent Yield across two years: average 80%+/-11% for 21 students

Percent Purity via titration analysis in first year: -12% error (less than theoretical); implemented improved estimation of endpoint – see Instructor Notes

Added IR Spectroscopy Tables (given values, and a blank one to fill in on report). Without these 'lead by the nose' guides, students did a poor job demonstrating understanding of the meaning of the IR spectra. This is most likely due to the fact that this is their first exposure to IR spectroscopy (second-semester freshman level).

Description: 

Synthesis of ammonium decavanadate, and analysis via IR, UV-Vis and quantitative titration. Time: 1.5 lab periods

 

Purpose

            The purpose of this lab experiment is to expose students to the synthesis of a colored POM, and to connect the use of standard analytical techniques to this new type of compound. It introduces the use of IR spectroscopy of inorganic materials.

 

Introduction

            Ammonium decavanadate ((NH4)6V10O28•6H2O) is an example of a polyoxometallate (POM). POMs are a large and diverse group, containing various metal cations, including, but not limited to, vanadium, molybdenum, chromium and iron. They are formed spontaneously in solution through what is called ‘self-assembly’. Essentially, they come together in solution through unknown mechanisms. In the lab, we can isolate various POMs by controlling conditions to favor one form over another, by varying concentration, pH or counter-ion. In the phase diagram of vanadates (Figure 1), one can see how varying pH and vanadium concentration can yield monomeric vanadate (VO43-), or POMs containing 2-10 vanadium atoms.

Decavanadate in Geology

            The decavanadate anion occurs naturally in minerals, huemulite Na4Mg2V10O28•24H2O, hummerite (KMg)2V10O28•16H2O, lasalite (NaMg)2V10O28•20H2O , pascoite Ca3V10O28•16H2O, magnesiopascoite Ca2MgV10O28•16H2O, and rauvite Ca(UO2)2V10O28•16H2O, which differ in the cations and amount of hydration. As you can see from Figure 3, the dominant color is yellow-orange. This is due to the presence of the decavanadate anion, which is yellow-orange. All of the vanadium POMs and vanadate are yellow-orange due to charge-transfer bands in the 200 – 500 nm range.

Decavanadate in Biology

            Vanadate (VO43-) is isostructural and isoelectronic with phosphate (PO43-). For this reason, vanadate has found interest with researchers studying the role of phosphate in biological systems, such as in insulin uptake in cells. In addition, decavanadate has been used to bind to biologically relevant molecules, such as gelatin, cytosine, estrogen receptor, and myosin.

 

Laboratory Experiment

In this experiment, students synthesize ammonium decavanadate, and analyze the resulting product via UV-Vis and IR spectroscopy as well as by permanganate titration.

Corequisites: 
Prerequisites: 
Learning Goals: 
  1. The student will define polyoxometallates (POMs).
  2. The student is able to interpret a concentration-pH diagram to determine conditions suitable for formation of the desired product.
  3. The student will apply IR spectroscopy to identify inorganic compounds.
  4. The student will use Beer’s Law to analyze the purity of a colored compound.
  5. The student will use redox titration to analyze a compound for purity.
Course Level: 
Equipment needs: 

Materials for a class of 20:

Ammonium metavanadate (NH4VO3, CAS#7803-55-6, Aldrich 99%): 6.0g

50% acetic acid solution: 100 mL

95% ethanol: 360 mL

Oxalic acid dihydrate (H2C2O4•2H2O, CAS#6153-56-6, Aldrich 99%):  2.5g

1.0 M sulfuric acid: 1.2 L

Sodium bisulfite (NaHSO3, CAS#7631-90-5, Aldrich):   2.0g

0.10 M potassium permanganate (KMnO4): 100 mL

50 mL beakers, 100 mL volumetric flasks, funnels and erlenmeyers

50 mL burets, 10.0 mL and 20.0 mL transfer pipettes

UV-Vis (Spec 20 is fine) and IR spectrophotometers

Implementation Notes: 

Because the synthesis is quick, but the crystals should be allowed to dry, I pair this experiment with another synthesis and analysis experiment, and spend the first lab period on the two syntheses, then the subsequent lab periods on analyses. If you have another experiment that takes 1.5 lab periods, then you can pair appropriately. The 0.5 lab period part is the synthesis. See Instructor Notes for other comments.

Time Required: 
1.5 - 4 hour lab periods (0.5 lab period for synthesis, 1 lab period for analyses)
24 Jun 2013

Lattice Systems Origami

Submitted by Jeremiah Duncan, Plymouth State University
Evaluation Methods: 

Through the course of the exercise, students populate a table with the geometries and symmetry elements of each crystal system. The instructor can review these tables with students in class. In addition, templates without labels have been provided that can be used to quiz students.

Evaluation Results: 

I have not formally assessed this activity, though I used it once to introduce crystal systems to my Junior/Senior level Inorganic chemistry course. The activity was well received; students took their 3-D paper models home, and some later told me they saved them and used them to study for the exam. I will teach this class again in Spring 2014, at which time I will more formally assess the activity.

Description: 

Covers the geometries and symmetries of the seven crystal systems in an inquiry-based manner. 2-D paper templates are provided, which the students cut out, fold, and tape together to create 3-D representations of the seven crystal systems: triclinic, monoclinic, orthorhombic, tetragonal, rhombohedral, hexagonal, and cubic. The students can then use these to determine the geometries and symmetries of the systems for themselves.

Learning Goals: 

In this activity, a student will:

  1. Determine the geometries of the seven crystal systems.
  2. Identify the following symmetry elements in a 3-D system: rotational axis and mirror planes.

     

Corequisites: 
Equipment needs: 

printouts of the templates

scissors

tape (recommended) or glue

Prerequisites: 
31 May 2013

Lithium Diazenide Surprise!

Submitted by Maggie Geselbracht, Reed College
Evaluation Methods: 

During conference, I gave students direct feedback on the MO diagrams and cartoons of MO surfaces their groups had drawn on the board.  As this conference was scheduled the day before a problem set was due, this feedback was helpful to students in gaining confidence drawing MO diagrams of diatomics. 

I collected the discussion questions and graded these on a 10 point scale, 1.5 points for question 1, 0.5 point for question 3, 3 points for question 7, 1 point for questions 2, 4, 5, and 6, and 1 point for effort.

Evaluation Results: 

Out of the 15 students that turned in written answers, 6 (40%) earned 9-10 points, 5 students (33%) earned 6.5-7 points, another 2 students (13%) earned 5-5.5 points, and 2 students (13%) earned < 5 points.  On the MO diagrams, I told them I did not care if they invoked sp­-mixing or not in their diagrams, but that they needed to be consistent with their choice.  In other words, if the 3 sg energy level was shown above the 1 πu energy levels in their diagram, then I expected to see evidence of sp­-mixing in their molecular orbital surface cartoons.  About half of the students chose to use sp­-mixing in their diagrams, but most of them did not show evidence of sp­-mixing in the molecular orbital surfaces.  Others that chose to invoke sp­-mixing did not shift the MO energy levels correctly; the common mistake was elevating the 2 su* energy level above the 1 πu energy levels rather than the 3 sg energy level.  Nearly all students that have read this paper find it approachable and understand the major conclusions and how these were reached after the discussion.

 

Description: 

Students in a sophomore-level inorganic chemistry course were asked to read the paper “High-Pressure Synthesis and Characterization of the Alkali Diazenide Li2N2” (Angew. Chem. Int. Ed. 2012, 51, 1873-1875. DOI: 10.1002/anie.201108252) in preparation for a class discussion.  For many students, this was a first exposure to reading the primary literature. 

In this paper, the authors describe the surprising stability of lithium diazenide, Li2N2.  In contrast with the increasing stability of peroxides and superoxides with the heavier alkali metals, the first alkali metal diazenide that was isolated was not the rubidium or cesium salt but rather the lithium salt (hence the surprise)!  The black, metallic-looking Li2N2 was synthesized at high pressure and high temperature by the decomposition of lithium azide, LiN3.  The crystal structure of Li2N2 was determined by Rietveld refinement of powder X-ray diffraction data and relevant bond distances were compared to diazene, H2N2, and the alkaline earth diazenides, CaN2, SrN2, and BaN2.  The authors also report evidence from infrared spectroscopy of nitrogen-nitrogen bonds in Li2N2.   Electronic band structure calculations suggest metallic behavior for Li2N2 and antibonding characteristics for the conduction electrons consistent with the molecular orbital description of the isolated diazenide ion.

Course Level: 
Prerequisites: 
Corequisites: 
Learning Goals: 

After reading and discussing this paper, a student will be able to:

  • Articulate the underlying problem and motivations driving the research presented in the paper.
  • Explain the collection of experimental data that lead to figures and tables presented in the paper.
  • Describe the important conclusions of the paper and the evidence presented by the authors to support these conclusions.
  • Gain confidence reading a paper from the primary literature in inorganic chemistry.
  • Describe periodic trends in the descriptive chemistry observed for the alkali metals with oxygen and for the alkali metals with nitrogen.
  • Interpret images of a unit cell to deduce stoichiometry and notable coordination features of an extended structure.
  • Draw the molecular orbital diagram of a homonuclear diatomic species and use the MO diagram to predict the bond order and magnetic properties of the diazenide ion.
Implementation Notes: 

Students in a sophomore-level inorganic chemistry course read the paper "High-Pressure Synthesis and Characterization of the Alkali Diazenide Li2N2" prior to a class discussion, held during a conference session.  A link to the pdf file was posted to the course Moodle, and students were asked to complete the short list of discussion questions (attached below as a Word document) prior to coming to conference.  I also used the Jmol resource embedded in a course Moodle page to display the unit cell of the Li2N2 structure (the pdb file that I used as the input for Jmol is attached below.) On the Moodle page with the Jmol structure, I told students, “Sorry, I don't know how to make Jmol draw the boundaries of the unit cell!  To guide your eye, there are lithium atoms (in lavendar) at all 8 corners of the unit cell.”  This Jmol model was intended to help students answer questions 4 and 5 in the attached list of questions in addition to Figure 2 from the paper.

I used this learning object during the past two years at different times during my course.  In Spring 2012, the paper was assigned in week 4 of the semester, after covering periodic trends in atomic properties, ionic structures, unit cells, stoichiometries of extended structures, basic X-ray powder diffraction, and Lewis structures.  In Spring 2013, the paper was assigned in week 9 of the semester, after MO theory of diatomics was also covered in addition to the previous topics.  The attached discussion questions were from the Spring 2013 version.

During conference, we used the discussion questions as a guide to walk through the paper.  I explained to students how to access the Supporting Information for a paper and the varying utility of this information, depending on the article.  In this case, the Supporting Information is quite helpful, and we talked through key figures and tables in both the paper and in the Supporting Information.  We also discussed the synthesis, and I answered some questions on the characterization methods, explaining briefly what Rietveld refinement is and how the results in Table 1 and Figure 1 are correlated.  For more information on the Rietveld refinement method, see the Web Resource on Powder Diffraction Crystallography Instructional Materials.  Finally, we took the last 10 minutes of conference, and I made all the students get up and in small groups, draw the MO diagram and molecular orbital surfaces for (N2)2– on the white boards around the room.  I circulated and made comments and corrections to each group on their MO diagrams.  

I also used this paper for one student as part of our Junior Qualifying Exam in Inorganic Chemistry.  In this format, the student has 3 days to read the paper and learn about it before taking a 30 minute oral exam, which takes the form of a question-and-answer based discussion of the paper.  For the Junior Qual, we spent most of the time discussing the diffraction analysis of the material, molecular orbital theory of the diazenide ion, and a brief discussion of the properties of lithium diazenide.

Finally, although I have not done so yet, I intend to use this paper in my Advanced Inorganic Chemistry course where we cover the electronic band structure of extended solids in more detail. Our discussions in Advanced I-chem are based on Roald Hoffmann’s book, Solids and Surfaces: A Chemist’s View of Bonding in Extended Structures.  The details of the Li2N2 electronic band structure calculations provided in the Supporting Information for this paper are an excellent illustration of many of the key concepts presented in Hoffmann’s book.

Time Required: 
50 minutes
9 Apr 2013

The Guided Tour of Metalloproteins

Submitted by Anthony L. Fernandez, Merrimack College
Description: 

Bob Morris of the University of Toronto created this website when he was teaching a class on Bioinorganic Chemistry.  It is takes the user through a guided tour of twenty metalloproteins that would commonly be used in a classroom when teaching the subject.  There are many JMOL figures of the protein and for each metalloprotein there are a sequence of structures that  take the user step-by-step through the metalloprotein and the active site.  (This is a real strength of ths site.)  There are links to the primary literature and the PDB for each structure.  

Prerequisites: 
Course Level: 
Corequisites: 
Subdiscipline: 
Implementation Notes: 

For my spohomore level class, I mainly use this as a resource when I teach "Applications of Coordination Chemistry" but I could also assign a tour of a given metalloprotein to my students.

For my advanced Bioinorganic course (a 2-credit elective), I would assign this as background material for the students.  I would also have them use this site as a model for how I want them to work through the metalloproteins that they dicsuss in class.  

I have not figured out any learning obejcts for this site site, but when I do I will be sure to post them to the site.

1 Apr 2013

Online Courses Directory

Submitted by Adam R. Johnson, Harvey Mudd College
Description: 

This website is a free and comprehensive resource that is a collection of open college courses that spans videos, audio lectures, and notes given by professors at a variety of universities. The website is designed to be friendly and designed to be easily accessed on any mobile device.

Course Level: 
Prerequisites: 
Corequisites: 
7 Jan 2013

Solid State Models with ICE Solid State Model Kits

Submitted by Katherine Nicole Crowder, University of Mary Washington
Evaluation Methods: 

Answers are evaluated for correctness. Please see key for answers.

 

 

Evaluation Results: 

Students always seem to have difficulty drawing the 3-D structures in 2-D.

They generally do very well on the assignment. Misconceptions typically arise in the number of nearest neighbors for the different ions and in the fluorite structure (since the ions are not in their typical locations).

Description: 

In this in-class activity, students are broken up into teams of 4, which are then sub-divided into two teams of two for the building of the structures. The activity makes use of the ICE Solid State Model kits, and each group should have their own full kit.

The activity has 6 sets of structures for the teams to build; depending on the length of your class, you could have each team build all six sets OR have each team build one of the six sets to then share with the rest of the class.

A - HCP and CCP

B - Primitive cubic and CsCl

C - NaCl (FCC) and NaCl (along the body-diagonal, shows the ABCA pattern well)

D - Fluorite and Anti-Fluorite

E - Zinc Blende and Wurtzite

F - Diamond and Graphite

There are related questions to answer for each of the structures built.

Learning Goals: 

A student will be able to recognize packing patterns and unit cells within solid state models.

A student will gain an understanding of packing/hole filling in ionic structures through classic solid state examples (NaCl, CaF2, ZnS).

Corequisites: 
Course Level: 
Equipment needs: 

Institute for Chemical Education (ICE) Solid State Model Kits for each team.

Prerequisites: 
Implementation Notes: 

I have run this as a dry lab and had each team build all six sets of structures; this usually takes the full 2.5 hour time block.

I used it as an in-class activity this year and had each of my six teams build one set of the structures to share with the rest of the class. This way they got experience building the models (for hands-on learners) but can use the models built by others to answer the questions. I had the models available after class for students to come back to, if necessary, to answer any remaining questions before the assignment was due.

The spacer rods seem to give the most problems in constructing the models (graphite, diamond, ZnS), so try to be sure that they are pre-cut to the proper length before running the activity.

Time Required: 
1-3 hours
19 Jul 2012

ChemTube3D

Submitted by Anthony L. Fernandez, Merrimack College
Description: 

ChemTube3D is a website maintained by the University of Liverpool that has interactive 3D animations ans structures.  The content is broken up into several areas:

  • A Level;
  • Organic Reactions;
  • Structure and Bonding;
  • Polymers;
  • Solid State.

There is a lot of information on the site, and the information could be used in many courses.  The areas that I find most useful in my sophomore-level inorganic chemistry course.

  • Structure and Bonding -> Simple Molecular Orbitals
  • Solid State

I use the solid state animations in lecture and I encourage my students to use these when studying.  My students find these visualiztions quite useful.

In my advanced half-semester course in organometallic chemistry, I use and refer my students to the "Organometallic Chemistry" and "Enantioselective metal catalysts" (found the "Organic Reactions" section).

Prerequisites: 
Corequisites: 
17 Jul 2012

Colored Note Cards as a Quick and Cheap Substitute for Clickers

Submitted by Chris Bradley, Mount St. Mary's University
Evaluation Methods: 

Use of the cards gives a rough "eyeball" evaluation of student learning throughout a lecture. Using the cards, for me at least, also provides a gauge of attendance as well and also if it waxes or wanes during the class period.

Description: 

For many years I have resisted using clickers, mainly because at our university there is no standard universal clicker. I wanted to keep student costs as low as possible but also desired the type of live feedback during a lecture that clicker questions can provide. In both my general chem. (200-300 students) and upper division courses (50-75 students), I now pass out 4 or 5 colored notecards on the first day of class and make sure everyone has one of each color. I then do clicker style questions and color code the different answer choices in powerpoint and ask them to hold up their choice after 15-60 seconds depending on the question. This has worked well to provide me instant feedback on difficult topics and doesn't end up singling out any particular student, which most students detest in larger lecture courses.   

 

Learning Goals: 

Students are able to provide feedback to the instructor on questions quickly and "anonymously" and allow one to adjust the direction of a lecture on the fly.   

Prerequisites: 
Corequisites: 
Equipment needs: 

NA

Implementation Notes: 

I typically use between 4-6 clicker questions during a 50 minute lecture. I'm sure someone could use more/less based on an individual's needs. I think the key is to use clicker style questions from the beginning of the class on a daily basis to remind students to bring the note cards in a book/binder/bag. This is really the only problem I have encountered- students often forget their cards. It is probably a wash though, as I'm sure students can also forget clickers.  

Time Required: 
1-5 minutes (depending on the problem)

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