Ammonia, NH₃

Calculation method | B3YLP

Basis set | 6-31G(d,p)

Final energy E(RB3LYP) in (au) | -56.55776873

RMS gradient (au)? 0.00000485

Point group of your molecule? C3V

Optimised Bond length (Å) = 1.01798

Optimised Angle (°) = 105.741

         Item               Value     Threshold  Converged?
 Maximum Force            0.000004     0.000450     YES
 RMS     Force            0.000004     0.000300     YES
 Maximum Displacement     0.000072     0.001800     YES
 RMS     Displacement     0.000035     0.001200     YES

NH3 Optimised Molecule

The optimisation file is given here.

Bond Vibrations

Bond Mode Number	1	2	3	4	5	6
wavenumber cm^-1	1089	1694	1694	3461	3590	3590
symmetry	A1	E	E	A1	E	E
intensity arbitrary units	145	14	14	1	0.3	0.3

I expected 6 modes of vibration from the 3N-6 property of virbations.
Both pairs of wavenumbers at 1693 cm-1 (Modes 2 and 3) and 3589 cm-1 (Modes 5 and 6) have the same energy.
Modes 1, 2 and 3 are bending vibrations.
Modes 4, 5 and 6 are stretching vibrations.
Mode 4 is a highly symmetrical stretch vibration.
Mode 1 is the "umbrella" stretch.
I would expect to see two bands in the spectrum of gaseous ammonia, one of those for Mode 1 and the other for the degenerate vibrations of Mode 2 and 3.

NH₃ charges

I expected the Nitrogen atom's charge to be negative and the Hydrogen atom's charge to be positive since the Nitrogen atom is more electronegative hence it will pull more of the electron density in each of its bonds closer to its own atom.

Atom Type	Nitrogen	Hydrogen
Charge	-1.125	+0.375

Nitrogen, N₂

Calculation method | B3YLP

Basis set | 6-31G(d,p)

Final energy E(RB3LYP) in (au) | = -109.523591113

RMS gradient (au)? = 0.0247

Point group of your molecule? D*H

Optimised Bond length (Å) = 1.09200

         Item               Value     Threshold  Converged?
 Maximum Force            0.000001     0.000450     YES
 RMS     Force            0.000001     0.000300     YES
 Maximum Displacement     0.000000     0.001800     YES
 RMS     Displacement     0.000000     0.001200     YES

N2 Optimised Molecule

The optimisation file is given here.

Bond Vibrations

Bond Mode Number	1
wavenumber cm^-1	2457
symmetry	SGG
intensity arbitrary units	0

N₂ charges

Atom Type	Nitrogen	Nitrogen
Atom Position	Left	Right
Charge	0.000	0.000

Hydrogen, H₂

Calculation method | B3YLP

Basis set | 6-31G(d,p)

Final energy E(RB3LYP) in (au) | = -1.15928019702

RMS gradient (au)? = 0.0971

Point group of your molecule? D*H

Optimised Bond length (Å) = 0.0600

         Item               Value     Threshold  Converged?
 Maximum Force            0.000000     0.000450     YES
 RMS     Force            0.000000     0.000300     YES
 Maximum Displacement     0.000000     0.001800     YES
 RMS     Displacement     0.000001     0.001200     YES

H2 Optimised Molecule

The optimisation file is given here.

Bond Vibrations

Bond Mode Number	1
wavenumber cm^-1	4465
symmetry	SGG
intensity arbitrary units	0

H₂ charges

Atom Type	Hydrogen	Hydrogen
Atom Position	Left	Right
Charge	0.000	0.000

Nitrogen Bond, N₂ Analysis

The molecule used to analyse the Nitrogen Triple bond was called DIDNAF.

The link is given below - https://bit.ly/2VpJrP9

A Jmol applet is shown below:

DIDNAF Molecule

The bond length for DIDNAF is larger than the computated bond length from N₂. This is because the Nitrogen atom in the TM complex is bonded to the metal atom, hence the bond has smaller energy and causes the bond length to be longer.

Haber-Bosch Process

The following values are calculated to work out the energy of the reaction
N₂ + 3H₂ -> 2NH₃

All values are given in atomic units (a.u) before conversion to kJ/mol

E(NH₃)= -56.55776873
2*E(NH₃)= -113.11553746
E(N₂)= -109.523591113
E(H₂)= -1.15928019702
3*E(H₂)= -3.47784059106
ΔE=2*E(NH₃)-[E(N₂)+3*E(H₂)]=

in kJ/mol (multply by 2625.5) = -299.58466 kJ/mol

The ammonia product is more stable than the gaseous reactants.

Nitrogen trifluoride, NF₃

Calculation method | B3YLP

Basis set | 6-31G(d,p)

Final energy E(RB3LYP) in (au) | -354.03254421

RMS gradient (au)? = 0.07304523

Point group of your molecule? = c3v

Optimised Bond length (Å) = 1.28000

Optimised Angle (°) = 109.471

         Item               Value     Threshold  Converged?
 Maximum Force            0.000164     0.000450     YES
 RMS     Force            0.000108     0.000300     YES
 Maximum Displacement     0.000613     0.001800     YES
 RMS     Displacement     0.000296     0.001200     YES

NF3 Optimised Molecule

The optimisation file is given here.

Bond Vibrations

Bond Mode Number	1	2	3	4	5	6
wavenumber cm^-1	482	482	644	930	930	1062
symmetry	E	E	A1	E	E	A1
intensity arbitrary units	1	1	3	208	208	40

NF₃ charges

Atom Type	Nitrogen	Flourine
Charge	+0.660	-0.220

Marking

Note: All grades and comments are provisional and subject to change until your grades are officially returned via blackboard. Please do not contact anyone about anything to do with the marking of this lab until you have received your grade from blackboard.

Wiki structure and presentation 1/1

Is your wiki page clear and easy to follow, with consistent formatting?

YES

Do you effectively use tables, figures and subheadings to communicate your work?

YES

NH3 1/1

Have you completed the calculation and given a link to the file?

YES

Have you included summary and item tables in your wiki?

YES

Have you included a 3d jmol file or an image of the finished structure?

YES

Have you included the bond lengths and angles asked for?

YES

Have you included the “display vibrations” table?

YES

Have you added a table to your wiki listing the wavenumber and intensity of each vibration?

YES

Did you do the optional extra of adding images of the vibrations?

YES

Have you included answers to the questions about vibrations and charges in the lab script?

YES - good explanations, well done.

N2 and H2 0.5/0.5

Have you completed the calculations and included all relevant information? (summary, item table, structural information, jmol image, vibrations and charges)

YES

Crystal structure comparison 0.5/0.5

Have you included a link to a structure from the CCDC that includes a coordinated N2 or H2 molecule?

YES

Have you compared your optimised bond distance to the crystal structure bond distance?

YES

Haber-Bosch reaction energy calculation 0.5/1

Have you correctly calculated the energies asked for? ΔE=2*E(NH3)-[E(N2)+3*E(H2)]

YES

Have you reported your answers to the correct number of decimal places?

no - you should have reported the energy to 1 d.p maximum.

Do your energies have the correct +/- sign?

YES

Have you answered the question, Identify which is more stable the gaseous reactants or the ammonia product?

YES

Your choice of small molecule 2/5

Have you completed the calculation and included all relevant information?

YES

Have you added information about MOs and charges on atoms?

It looks like you ran out of time, and only managed to report the charges.

Independence 0/1

If you have finished everything else and have spare time in the lab you could: Check one of your results against the literature, or Do an extra calculation on another small molecule, or Do some deeper analysis on your results so far

Ammonia, NH3

Nitrogen, N2

Hydrogen, H2

Nitrogen Bond, N2 Analysis

Haber-Bosch Process

Nitrogen trifluoride, NF3

Marking

Wiki structure and presentation 1/1

NH3 1/1

N2 and H2 0.5/0.5

Crystal structure comparison 0.5/0.5

Haber-Bosch reaction energy calculation 0.5/1

Your choice of small molecule 2/5

Independence 0/1

Ammonia, NH₃

Nitrogen, N₂

Hydrogen, H₂

Nitrogen Bond, N₂ Analysis

Nitrogen trifluoride, NF₃