The document discusses molecular modeling as a teaching tool that allows students to understand molecular behavior and properties. It highlights the significance of electron density and electrostatic potential models in elucidating atomic positions, bonding, and interaction energies within molecules. These models enhance synthesis and analysis in chemistry by providing visual representations of molecular characteristics and reactivity.

1. MOLECULAR MODELLING
By sreeremya.s
Asst professor,sree narayana guru
college,cbe

2. • Models allow students to “think like a
molecule”.
• Students “see” what a molecule sees and
“feel”
• what a molecule feels. Models provide a
window
• on the molecular world.

3. • Molecular modeling is a tool for achieving these
goals.
• Synthesis and analysis are experimental. They
cannot
• (and should not) be done away with. However,
• modeling does change the way we do syntheses
and
• analysis. And, it speaks directly to the intellectual
goals
• of chemistry.

4. • Electron Density Models
• Electron density models show the locations of
• electrons. Large values of the density will first
reveal
• atomic positions (the X-ray diffraction
experiment)
• and then chemical bonds, while even smaller
values
• will indicate overall molecular size.

5. • To Bond or Not to Bond
• Unlike conventional structure models which
require
• bonds to be drawn explicitely, electron density
models
• may be used to elucidate bonding. For example,
the
• electron density model for diborane shows that
the
• borons are not bonded.

6. Electrostatic Potential Models
The electrostatic potential is the energy of
interaction
of a point positive charge (an electrophile)
with the
nuclei and electrons of a molecule. Negative
electrostatic potentials indicate areas that are
prone to
electrophilic attack. For example, a negative
electrostatic potential of benzene shows that
electrophilic attack should occur onto the p
system,
while the corresponding electrostatic potential
for
pyridine shows that an electrophile should
attack the
nitrogen in the s plane.

7. • Electrostatic Potential Maps
• The electrostatic potential can be mapped onto the
• electron density by using color to represent the value
• of the potential. The resulting model simultaneously
• displays molecular size and shape and electrostatic
• potential value. Colors toward “red” indicate negative
• values of the electrostatic potential, while colors
• toward “blue” indicate positive values of the potential.