Second year

4 Jan 2008

In Lewis' Own Words

Submitted by Nancy Scott Burke Williams, Scripps College, Pitzer College, Claremont McKenna College
Evaluation Methods: 

See implementation notes. What I evaluate is the sorts of questions and answers the students generate both on their own and in the discussion.

Evaluation Results: 

I've been very impressed by the level of discussion this generates. The students love the paper for its readability, the "outdated" ideas, and the cleverness of the hypotheses put forth. They are very good at putting themselves in Lewis' position, knowing what he did, and the discussion quickly developed (this year) to a surprisingly deep discussion of the nature of scientific truth, the iterative scientific method, and the role of theory and experiment. The students "get" these models, and can see how powerful they are even though they are "wrong". I finished by emailing them Bronowski's incredibly powerful monologue on scientific knowledge: 

 

Description: 

This is G. N. Lewis' classic paper explaining his "octet rule" and the idea of bonds being represented as shared electron pairs.  It's beautifully written, and is a lot of fun for students to read.  Highlights include his description of atoms as being concentric "cubes" of eight electrons at the vertecies, philosophical discussions of the importance of letting experimental observations guide the development of theory, and the sense that students gain that Lewis developed this theory completely in the absence of an orbital or Bohr-type model of the atom.  It wonderfully captures the way in which a brilliant mind wrestled with the problems of developing a bonding theory for the periodic table.  Students understand the paper pretty easily, and are capable of picking out little "gems" on a first read of their own which they bring to a discussion.  

Prerequisites: 
Corequisites: 
Learning Goals: 

Students should be able to address the following questions:

(1) Explain Lewis' original "cube model" and his subsequent "tetrahedron model" of the atom.

(2) Why does Lewis abandon his first for his second model in this paper, even though it contradicts the prevailing theory of the day.

(3) Compare and contrast what Lewis actually proposed with the "Lewis Dot Model" which youlearned in genchem. 

(4) Please discuss the usefulness of  low-level theory which is easy to use vs. high-level theory which is hard to use, and articulate the value (or lack thereof) of doing things at a "simplistic" level.

Implementation Notes: 

I hand out this paper in advance of one class and have the students bring the answers to the questions in the handout as well at three questions of their own, which they give to another student. By the next class, they try to answer those student questions, and we use all of the questions so generated as a basis for a full class discussion.

Time Required: 
5 minutes on one day, plus one additional day for discussion (students read beforehand)
18 Nov 2007

Point groups and character tables

Submitted by Joanne Stewart, Hope College
Evaluation Methods: 

I collect and grade the handouts.

Evaluation Results: 

The students usually do this activity in small groups. The good thing about doing this in class is that misconceptions arise and can be addressed immediately. I will post a summary of the grading results when I do this activity next spring (2010).

Description: 

Students practice assignment of symmetry elements and point groups, practice developing a character table, and learn about the link between orbitals and irreducible representations.

Learning Goals: 

Students will be able to sketch and label the symmetry elements for a simple molecule.

Students will be able to use a flow chart to assign the point group of a molecule.

Prerequisites: 
Equipment needs: 

None.

Corequisites: 
Course Level: 
Implementation Notes: 

Instead of collecting the handouts, you can ask the groups to "report out" their results to the rest of the class by writing their answers on the board and explaining them. This adds about another 15 minutes to the activity.

Time Required: 
30 minutes
18 Nov 2007

Lewis structures and formal charges

Submitted by Joanne Stewart, Hope College
Evaluation Methods: 

I collect and grade the worksheet.

Evaluation Results: 

Most students are able to complete the worksheet correctly.

Description: 

This is a worksheet on Lewis structures and formal charges. The learning goal is for students to be able to use formal charges to defend the relative stabilities of resonance structures of molecules.

Learning Goals: 

1. Students will be able to draw resonance structures of molecules.

2. Students will be able to assign formal charges to atoms.

3. Students will be able to use formal charges to argue about the relative stability of various resonance structures.

Corequisites: 
Topics Covered: 
Equipment needs: 

None.

Course Level: 
Prerequisites: 
Time Required: 
20-25 minutes
18 Nov 2007

Descriptive Chemical Jeopardy

Submitted by Nancy Scott Burke Williams, Scripps College, Pitzer College, Claremont McKenna College
Description: 

Students assigned a portion of the periodic table.  Generally, a student is given a column of the main group, but this can easily be varied, depending on the size of the class.

 Students then submit Jeopardy-style questions (a statement, to which the "answer" can be stated in the form of a question) about each element in their portion of the table.  The instructor then breaks the questions into categories (Alex, I'll take obscure, toxic p-block elements for 500!).  The questions are then written on 3x5 cards, with the name of the submitter on the back.  Depending on class size, the class is then broken into 2-4 teams.  The submitter of a given question is prohibited from participating when his or her question is posed.  All answers must be given in the form of a question.

Prerequisites: 
Topics Covered: 
Corequisites: 
Equipment needs: 
Whiteboard, pens, someone who can whistle the "Jeopardy" theme.
Subdiscipline: 
Course Level: 
18 Nov 2007

From molecules to solids: Lewis structures

Submitted by Barbara Reisner, James Madison University
Description: 

I have students construct Lewis structures on the board starting at the noble gases and working backwards to the group 14 elements.  We talk about both second period then heavier elements.  As we move across the period we transition from molecular solids to extended solids.  

This is a nice transition from molecular chemistry to extended compounds.  I use this as a bridge into the solid state portion of the course because it allows me to review Lewis structures, trends in bond energies, and provide some descriptive chemistry information. 

 Need to think about assessment.

Subdiscipline: 
Prerequisites: 
Equipment needs: 
CrystalMaker or a viewer to see the files that I'll eventually construct.
Corequisites: 
Course Level: 
17 Nov 2007

What happens when chemical compounds are added to water?

Submitted by Barbara Reisner, James Madison University
Description: 

It’s very surprising how little students remember from general chemistry.  This assignment helps students make connections between the macroscopic properties of solutions and what happens at the molecular level.  This activity serves as a bridge between sections on acid-base chemistry and coordination chemistry.

Students are solicited for their models of the behavior of different chemical compounds in water in class and asked to put these models on the board.  We then look at the properties of these solutions (color, acid-base) and refine these models in class.

Students are then shown what happens when NaOH(aq) is added to NiCl2(aq) and asked to provide a molecular-level model.  Again, they put their models on the board and we discuss their models.

 I figure out what students have learned by asking a nearly identical question on an hour exam, the final, or both.

Subdiscipline: 
Topics Covered: 
Prerequisites: 
Equipment needs: 

50-mL Ehrlenmeyer flasks
graduated cylinder
pH meter

Corequisites: 
Course Level: 
17 Nov 2007

Looking at Solid State Structures

Submitted by Barbara Reisner, James Madison University
Description: 

I find that students get a better understanding of solid state structure by playing with models.  I give students two fifty-minute class periods to look at the structure types that we discuss in class.  This is an old in-class activity that needs massive updating.

In this activity,  students look at the holes in different lattice types (simple cubic, ccp, hcp) and the CsCl, NaCl, CdI2, ZnS, and spinel structure types.

In the past, I have not directly figured out if students did this other than going around the class and having students explain stuff to me and asking them related exam questions.

Prerequisites: 
Topics Covered: 
Corequisites: 
Equipment needs: 
Course Level: 
17 Nov 2007

Inorganic Chemistry and Art

Submitted by Lori Watson, Earlham College
Description: 

This activity provides a fun way of examining the historic use of inorganic compounds as pigments. Students learn about some of the pigments used in paintings, optionally researching particular artworks that use these pigments, and then make and use paints based on these inorganic compounds. This ­is an excellent “last day of the semester” activity.

 

There will be nice slides of the structures of some of these pigments and slides of famous painting which use them as soon as I can figure out how to upload a 66 MB file!!!

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Subdiscipline: 
Prerequisites: 
Equipment needs: 

Inorganic Chemistry and art:

Chemicals

Various inorganic compounds that are generally available in ores, or simply made from historically available ingredients. Some suggestions:

Pb3(SbO4)2

Pb3O4

Celadonite or Glaucinite (often the geology department will have plenty of this to give you): K[(Al, Fe3+)(Fe2+,Mg)](AlSi3, Si4)O10(OH)2

CdS

PbCrO4

Ag2CrO4

BaCrO4

ZnO

BaSO4

CoO×Al2O3

CoCl2

This is a good opportunity to “use up” some of the ancient bottles of inorganic salts that are not used in any current experiment that are in your stockroom or dusty cabinets.

Materials and equipment

Mortars and pestles

Plastic or glass stirring rods (some metals will discolor the paints)

Small canvases (purchased at a craft or art supply store)

Inexpensive paint brushes, several sizes (purchased at a craft or art supply store)

Lots of newspaper to protect lab surfaces

Eggs

Linseed oil (purchased at a craft or art supply store)

Corequisites: 
Course Level: 
17 Nov 2007
Evaluation Methods: 

In their lab notebooks, students are asked to qualitatively and quantitatively analyze all of the diffraction patterns and relate these to the unit cells of the crystal dot patterns on the optical transform slide.  This report in their notebook is graded and is the first of several "notebook reports." 

In years when all of the students in the lecture portion of the course are also in the lab, I follow-up with a problem set question such as the one linked above under Related Activities (viewable to VIPEr users with approved Faculty status).

Evaluation Results: 

Students easily grasp the concept that distances in the diffraction pattern are inversely related to distances in the crystal. They also readily see that the rotational symmetry of the crystal is also observed in the diffraction pattern.

 Understanding systematic absences due to centering and glide plane symmetries is a more difficult concept for them to grasp.  In particular, they are often confused when I ask them to draw centered vs. primitive unit cells for a particular crystalline pattern and that this refers to the periodic array that is the "crystal" and not the diffraction pattern.  This is a case where asking a follow-up question on centered lattices and the effects on diffraction patterns can be particularly useful. 

Description: 
­This activity introduces students to the symmetries of 2-D repeating patterns and X-ray diffraction. Using small lasers and Optical Transform slides (available from the Institute for Chemical Education), students qualitatively and quantitatively investigate the relationships between the sizes and symmetries of unit cells and the effects observed in diffraction patterns.
Prerequisites: 
Learning Goals: 

After exploring the diffraction of visible light from a variety of 2-D crystalline patterns, a student should be able to qualitatively and/or quantitatively describe:

  • The effect of changing the wavelength of the diffracted light on the diffraction pattern
  • The effect of changing the crystal spacing on the diffraction pattern
  • The effect of changing the crystal symmetry (i.e. 2-fold, 4-fold, 6-fold) on the diffraction pattern
  • The diffraction signatures of lattice centering and the presence of glide symmetry in the crystalline pattern
  • The determination of the unit cell size of the crystalline pattern from diffraction measurements

Course Level: 
Equipment needs: 
Optical Transform slides (available from the Institute for Chemical Education), HeNe lasers
Implementation Notes: 
See the attached document below for helpful hints and tips for the instructor.
Time Required: 
2-3 hours

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