Molecular Modeling of C, N, and O.
This exercise will provide direct experience in using molecular modeling
software to calculate wavefunctions for selected elements to obtain and
to interpret information from quantum mechanical predictions of specific
atomic properties. Spartan Student Software is available from any
network PC on the Winthrop campus; it can be accessed via the
Start,
All Programs, Chemistry and Biology, and selecting the "
Spartan
ST" program to run.
Multiplicity:
Multiplicity
is
the number of states available and must be determined prior to setting
up a wavefunction calculation:
-
For all paired electrons, singlet
-
For one unpaired electron, doublet (one up or one
down)
-
For two unpaired electrons, triplet (two up, one up
and one down, two down)
-
For three unpaired electrons, quartet (three up, two
up and one down, two down and one up, three down)
Carbon: Save the
C
Atom to your local drive, then open Spartan and load the saved file.
-
Select Setup, Calculations from the Menu
-
Select Hartree-Fock / 3-21G methodology (to be used
in determining wave functions)
-
Change the multiplicity to the correct value for a
carbon atom
-
Select the Print box marked Orbitals to ensure your
job output has the required information for this exercise.
-
Run the wavefunction calculation for carbon by selecting Submit
-
Once the calculation is completed, select Display, Output to
view the results; since carbon has unpaired electrons, the output should
separately list a set of energies (eigenvalues) and orbital coefficients
for each type of spin (alpha or beta)
-
Record [using either the atomic units (a.u.), or electron Volts (eV)] the
occupied energy levels for the carbon atom. Note:
1 atomic unit is equal to 27.21 eV; 1 eV = 96.49 kJ/mol.
-
Copy the carbon output file and paste into a text file and save on your
own drive.
-
Select Display, Properties, and record the volume
given in units of cubic Angstroms
Nitrogen and Oxygen: Save the
Nitrogen
Atom and
Oxygen Atom in separate files
to your local drive and repeat the set of steps done for carbon.
Answer the following:
1. Draw the electron configuration for each atom and identify
its multiplicity.
2. Compare the volumes for these three types of atoms; explain
the difference while also identifying the number of electrons in each type
of atom.
3. For each type of atom, tabulate energies for the set of occupied
electronic energy levels in ascending order.
4. Compare the lowest electronic energy level for each of the
three atoms and explain, using Coulomb's Law, the underlying reasons for
the observed differences.
4. Determine the ionization energy for each of these atoms in
units of both eV and in kJ/mole. Compare these results with the kJ/mole
table in the Appendix in your text. Based on these three atoms, what
conclusions would you make about how ionization energies change from left
to right across a row in the periodic table.
5. For the three atoms, examine closely the energies associated with
the three 2p orbitals and explain the underlying reason for the specific
three patterns that you observe (this question requires a little thinking....).
6. Please turn in a copy of the output file for your carbon atom only
with your set of answers....