Periodic trends

29 Jun 2015

Lewis Structure Challenge

Submitted by David A. Laviska, Rider University
Evaluation Methods: 

Ideally, a quiz should be given during the next lecture period (or another convenient time) following the in-class exercise. Given the format of the in-class activity, the quiz could include both traditional structures (e.g., SO42-) as well as criteria similar to those dispensed during the Lewis structure challenge activity. Additionally, mid-term and/or final examinations should include questions that revisit the skills involved in drawing accurate Lewis structures.

Evaluation Results: 

This is a new Learning Object that has been developed over the last several months and it has not yet been tested in the classroom.

Description: 

This in-class activity is designed to give general chemistry students practice with drawing Lewis structures. Small groups of 3-5 students compete for points by creating hypothetical molecules that meet criteria (numbers of elements and atoms) assigned by the professor. Beginning with simple molecules, the basic challenge format calls for increasingly complex criteria in successive rounds of competition. One optional variation also allows student groups to challenge each other for bonus points.

Learning Goals: 

Students will practice skills relating to

  • accurately representing bonding in simple molecules using the convention of Lewis Dot Structures.
  • recognizing the periodicity of valence electron configurations in Groups within the Periodic Table.
  • creating hypothetical molecules based on an understanding of valence shell electron configurations.
  • counting electrons in order to rationalize bonding patterns.
  • assigning formal oxidation numbers to covalently bonded atoms.
  • assigning formal charges on individual atoms.
  • identifying the presence of resonance structures and drawing them accurately.
Corequisites: 
Course Level: 
Prerequisites: 
Implementation Notes: 

The competition involves students working collaboratively within their groups to draw Lewis structures for hypothetical molecules. In successive rounds of competition, the instructor assigns criteria for the compounds to be drawn as outlined in the Faculty Guide (to be downloaded from this webpage). The students choose non-metal elements from the Periodic Table and attempt to construct valid Lewis structures that satisfy the criteria within a limited timeframe. Points per round are awarded for correct structures, with bonuses based on identifying ideal geometry and formal oxidation states as outlined in the Faculty Guide document. Each round should be timed (to be determined by the instructor, but generally kept short, e.g., 2-4 minutes, in order to add a time-pressure facet to the competition). After time has been called in each round, structures should be shared with the instructor for discussion and immediate awarding of points. Additional strategies and notes are discussed in the Faculty Guide document.

Time Required: 
At least one class period
10 Jun 2015

The Orbitron

Submitted by Barbara Reisner, James Madison University
Description: 

Do you want to show your students beautiful illustrations of atomic orbitals? My favorite place to go is the Orbitron, Mark Winter's gallery of AOs and MOs on the web. Not only can you see images, but you can link to different representations of the wave functions and electron density functions.

Flash is required for this site.

Prerequisites: 
Corequisites: 
10 Jun 2015

Web Resources from the 2013 Inorganic Curriculum Survey

Submitted by Barbara Reisner, James Madison University

 

In the 2013 Inorganic Curriculum Survey, respondents were asked about the resources they used when they teach inorganic chemistry. About 20% of respondents selected "other" and provided information about these resources. A number of people mentioned specific websites. This collection consists of the websites submitted in the survey.

Prerequisites: 
Corequisites: 
25 Jan 2015

Periodically Periodic

Submitted by Barbara Reisner, James Madison University
Evaluation Methods: 

I award students credit for participation, not correctness. (These in class activities not only help the students work through the material, but they also encourage them to be there for an 8 AM class 3 days a week.) If students participate in 75% of the in class activities, they get full credit for this 5% part of their grade. (I only require 75% because I don't have to keep track of student absences for university activities, illness, misset alarms, etc.)

I read over these every night, make notes on things that I think are significant problems, and return them the following class period. If I see anything that is a consistent problem, I'll discuss it at the beginning of the following class period.

Evaluation Results: 

Students have no trouble stating the trends, but they have more problems explaining the arguments. I find that  they tend to make incomplete or incorrect arguments arguments. For example, 

  • the radius is smaller as you go across a period because Z increases
  • Z* increases because sheilding increases
  • the size of the atom increases because the radius is larger

There is also a tendency to go back to the "it's extra stable because of the half-filled or completely filled subshell" that they learn in general chemistry. 

While the students are working, I find it really valuable to sit down and discuss how to make a more complete argument about periodic trends.

Description: 

I like having students look at data and then explain data based on what they know about periodic trends. This activity uses the data we all use for radii and ionization energies and asks students to look just a little bit deeper. 

I have gone back and forth between using this as an in class activity (my current practice) and using some of these questions on exams. 

Learning Goals: 

A student will be able to

  • use experimental data to identify periodic trends; and
  • provide complete explanations for the periodic trends observed in experimental data using Z*, n and electron configuration arguments.
Equipment needs: 

NA

Prerequisites: 
Corequisites: 
Course Level: 
Topics Covered: 
Implementation Notes: 

Currently, I use this as an in class activity in my lower division class; the first two pages take an entire class period (with interspersed lecture). I use this as review when I teach the second semester (which is separated in time from the lower division class). The seniors finish this activity in the class period.

I begin class by asking students to answer things based on what they remember from general chemistry, then to look at the data and use the explanations we've discussed (size - based on shells of electrons, Z* and electron configurations where things aren't always changing in the same way) to explain these periodic trends. (I've only started the learning cycle bit this year. I've found that my students have persistent misconceptions from general chemistry / high school. I'm hoping that by letting them acknowledge these ideas and discuss where they fall down may help their understanding and retention of the material.)

After the brief instructruction and introduction to the activity, I have students work in groups of three. (They have assigned groups for the whole semester.) My two peer leaders and I go around and answer questions when they come up. If I hear the same question a few times, I'll bring the class together to talk about the question. (I use Doceri so that's pretty easy to do from anywhere in the room.)

I try to leave 5 minutes to wrap up at the end of class.

Time Required: 
50 minutes (although more would be nice to get to page 3)
9 Dec 2014
Evaluation Methods: 

I assigned this paper as a 10-point literature activity, intended mostly to expose students to the chemical literature and enhance their interest in class topics. Questions focus largely on reading comprehension, but could easily be expanded for use in a more advanced course (see implementation notes for some suggestions). Students answer the questions listed in the activity sheet to verify that they have read the paper, and I grade them largely based on participation. We took 10-15 minutes in class to discuss the interesting points of the paper (could easily be extended to a longer discussion if you have the time), but this was used as an independent activity to expose them to the ideas and enhance their interest in coordination chemistry. The paper is extremely readable, and students did not appear to have difficulty understanding it on their own. 

 

Evaluation Results: 

Though brief, the in class student discussion indicated a high level of interest in the paper, and excitement about a "real" application of course material. The reading question answers were largely correct and complete, indicating that students had achieved at least basic understanding of the paper, though some students had difficulty explaining how the authors used substitution experiments to infer Mg binding types.

Description: 

I use this literature discussion in my second year inorganic class as a follow-up to a lab experiment where students synthesize Werner complexes and then (with much guidance) analyze their IR spectra using symmetry and group theory arguments. This paper provides an excellent example of how cobalt complexes are used in modern applications, and serves as a bridge to bioinorganic chemistry, which is a central feature later in the course.

Rowinska-Zyrek, M.; Skilandat, M.; Sigel, R. Hexamminecobalt(III) – Probing Metal Ion Binding Sites in Nucleic Acids by NMR Spectroscopy Z. Anorg. Allg. Chem. 2013, 639 (8-9), 1313-1320. DOI: 10.1002/zaac.201300123

Prerequisites: 
Course Level: 
Corequisites: 
Learning Goals: 

In answering these questions, a student will:

- Gain a greater appreciation for the use of transition metal complexes in solving problems of structure and binding in biological systems.

-  Discuss specific features of cobalt hexammine complexes that allow them to substitute for magnesium hexaaqua complexes  when binding to biological molecules

-  Appreciate the effects of metal size, charge, lability, and spectral activity on the ease with which a system can be characterized

-  Identify the advantages and limitations of using a structural mimic to study molecular structure.

Implementation Notes: 

I passed this paper out in the week after students synthesized a series of Werner complexes in the laboratory. Students had been exposed to descriptive inorganic chemistry and periodic trends, symmetry and (rudimentary) group theory prior to this exercise.  In the second half of the laboratory session, they had compared the rates of hydration of hexammine, pentammine, and cis-tetrammine chloride cobalt complexes using UV/VIS, so some students were quite familiar with the stability of the hexammine complex. My students had not yet been introduced to ligand field theory, HSAB theory, redox mechanisms, or the 18-electron rule; incorporation of those ideas would be an interesting extension to the activity if your class has already been prepared to discuss those theories. The paper also explicitly mentions the large number of structures in the RCSB protein data bank that make use of cobalt complexation. This could be another option for extending the exercise for an upper-level course.

Most of the students in my class are juniors or seniors, despite the fact that this is a 200-level course. Many of them have had organic and biochemistry, and several are biochemistry majors. Biological applications are of great interest to them, and bioinorganic chemistry was one of the favorite topics of the course. Students were excited to see class topics applied to current research problems. This paper was a nice example to foreshadow more advanced topics, and later served as a familiar reference point for discussions of inner and outer sphere binding mechanisms, redox chemistry, catalysis, and bioinorganic chemistry.

 

12 Sep 2014

Maggie's LOs

Submitted by Chip Nataro, Lafayette College
Corequisites: 
Prerequisites: 
4 Aug 2014

A Living Syllabus for Sophomore Level Inorganic Chemistry

Submitted by Sheila Smith, University of Michigan- Dearborn
Description: 

In my sophomore level inorganic course, I have experimented with the idea of a living syllabus as a way to develop my own specific learning objectives and to help the students connect the material to the tasks that will be expected of them in assessing their learning. 

Learning Goals: 

The student will connect in class activities, lecture and discussion to the tasks that will be used to assess their learning.

Prerequisites: 
Course Level: 
Equipment needs: 

none

Corequisites: 
Implementation Notes: 

We took 2 minutes at the end of each lecture period to verbalize and record the specific learning objectives for the day.  (After this lecture, what exactly does the professor expect me to be able to DO…?)  On the few occasions when we ran over and did not get to this, we used the Course Management System (CMS) discussion feature to complete the task.  The syllabus was continually modified (added to) over the ourse of the entire semester.

17 Jul 2014
Evaluation Methods: 

This literature discussion developed at the 2014 IONIC VIPER workshop and has not been evaluated yet. 

Description: 

This is a literature discussion of a review by Tom O'Halloran (The link to the paper is included in the "Web Resources" below). The review covers concepts of metal content in cells, metal trasport, storage, and regulation. Its a good review to start a broader or deeper discussion about metals in biology. We have provided some questions to help guide the student discussion. These questions can be given to students prior to coming to class, and the answers can either be used for the in-class discussion and/or collected. 

Corequisites: 
Prerequisites: 
Learning Goals: 
Students will:
-- apply fundamental concepts from class material to literature examples, such as metal binding specificity (dependent on size, charge, etc.), Kd, strength of ligand binding, concentration and turnover of free ions 
-- gain an appreciation for the importance of transition metals in biological systems and the different roles metals play in the cell (metalloenzymes, metallochaperones and metalloregulatory proteins)
-- develop scientific reading comprehension in a guided activity
Implementation Notes: 

Access the manuscript through your library and provide a copy of the manuscript to the students along with the discussion questions a few days before class, and then have an in class discussion abou the chapter. 

Time Required: 
45 minutes (1 lecture) + student time prior to lecture
15 Jul 2014
Description: 

The Diatom Thalassiosira weissflogii is very resilient.  It thrives in poor quality water, where high CO2 levels, chlorine and cadmium ion concentrations, and pH are observed.  How is it possible for cadmium ions to be a nutrient for this diatom, when it is normally seen as a toxin in biological systems?

This LO introduces students to bioinorganic chemistry using the enzyme carbonic anhydrase to illustrate biodiversity, adaptation, HASB theory, metal ion ligand bonding as represented by the PDB using Ligand Explorer, and more.

Prerequisites: 
Corequisites: 
Learning Goals: 

Students will:

  1. be able to describe the function of three organic ligands that bind zinc and cadmium ions, namely glutathione, metallothionein and carbonic anhydrase.
  2. appreciate that different metal ions exhibit ligand atom binding preferences.
  3. be able to understand the linkage between bioavailability of elements driving survival through ligand adaptation.
  4. be able to understand the purpose of ligand metal ion binding as a way to enhance molecular functionality (carbonic anhydrase won't work without a zinc or cadmium ion present in the active site) and to prevent toxicity (having a metal ion coordinated to one of the three chelators listed under learning goal 1 above won't allow it to contribute to potential toxicity).
Course Level: 
Implementation Notes: 

This is a real life example of an organism adapting to it's environment by taking what is typically a toxic metal ion and using it to allow a key enzyme to function.  This LO can be used to introduce bioinorganic chemistry and/or after learning the basics of coordination chemistry, be a summary illustration of the application of what students have learned.  This is a new LO developed at the VIPEr workshop at Northwestern University, July 2014 so it is yet to be tested.  Please do so and post your feedback.

Time Required: 
20 minutes
Evaluation
Evaluation Methods: 

Students should answer the following questions having participated in the PowerPoint discussion:

 

Associate the role of each of the following ligands in biological systems by writing either sequestering agent or enzyme after each item below:

Glutathione

Carbonic Anhydrase

Metallothionein

 

Match the amino acid/ligand (Lewis Base) listed below with the preferred metal ions (Lewis acid) Cd2+ and Zn2+ (if you think there is no preference, state this):

Cysteine (S)

Histidine (N)

Water (O)

Bicarbonate (O)

 

How was the Carbonic Anhydrase “ligand” adapted to accommodate Cd2+ ions to allow diatoms to thrive in Zn2+ deficient waters?

 

Fill in the gaps below with either Zn2+ or Cd2+:

 

____ ions are thought to induce toxicity in cells by inducing oxidative stress.  ____ ions, however, are considered essential trace metal ions.

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