Virtual and tactile molecular models:Their complimentary nature in

Discovery-based general chemistry

Scott A. Sinex and Barbara A. GagePrince George’s Community College

Presented at the 228th American Chemical Society National Meeting in Philadelphia, PA

on 22-26 August 2004.

the chemist’s world of multiple representations…

C6H6

Are students still in flatland?

CH2CH2CH3

CH2CH3

Where are our students in this world?H

H

H C

H

H

H

C

H

H

C

H

H

C

H

H

C

the computer tools we use…

• ChemSketch – 2D chemical structure drawing (freeware)

• Chime/RasMol – molecular rendering (freeware) great for developing web-based activities

• Spartan – computational (expensive software)

All available in open computer labs !

H

H

H

H C

discovering

confirming and

verifying bond angles

discovering molecular geometry…

discovering molecular polarity…

H20 H2S OF2 SF2

CH20 SO3

Use of electrostatic

potential maps in Chime

discovering molecular distortions…Measure the bond angle (H-N-H) and explain any difference

Measure and explain the non-ideal bond angles in each

discovering molecular flexibility…

Are bond lengths and bond angle constant in a molecule?

Can the nitro

groups on ONC rotate around the C-N bond?

discovering intramolecular interactions…With model in hand, ask students how the two chlorine atoms would like to be oriented?

uncovering molecular complexity…

hemoglobin molecule

Type of protein structure?

How many helical chains?

Hydrogen bonding

the tactile model...

shows connectivity displays the real 3D in ideal state possibility of illustrating some

intramolecular interactions (internal rotation)

can test superposition of isomers can generate possible conformer

structures by internal rotation

the tactile model…

is rigid (set bond lengths and angles)

true molecule size and shape not possible

can fall apart! (at least some)

the virtual model…shows true arrangement plus distortions can change orientation and mode of

display including complicated molecules allows measurements provides flexibility – animated vibrations can generate animated reaction

mechanismscan display electrostatic potential maps

A GREAT DISCOVERY TOOL!!!

the virtual model…

may encounter incorrect structure files

may not grasp the 3D nature on flat computer screen

tactilemodels

virtualmodels

Enhanced understanding of molecular structure in general chemistry and

fosters a smooth transition into organic chemistry

in the end…

For further information see our course webpages plus-

Scott Sinex – http://academic.pgcc.edu/~ssinex

Barbara Gage – http://academic.pgcc.edu/~bgage

CONFCHEM Fall 2004 – Teaching Computing in Chemistry Courses Paper #5: Empowering Student Learning with Molecular Visualization Tools in Discovery-based General Chemistry

Thanks to MDL for Chime and ACD for ChemSketch!!!