Modjhl416
NH3 molecule
Optimisation of the molecule
Molecule name: NH3
Calculation method: RB3LYP
Basis set: 6-31G(d.p)
Final energy E(RB3LYP): -56.55776873au
RMS gradient: 0.00000485au
Point group: C3V
Bond distance: 1.01798
Bond 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
test molecule |
The optimisation file is linked to here.
Vibrations of the molecule
1. How many modes do you expect from the 3N-6 rule? 6
2. Which modes are degenerate (ie have the same energy)? Mode #5 and #6
3. Which modes are "bending" vibrations and which are "bond stretch" vibrations? Bending: #1,2,3 ; Stretching: #4,5,6
4. Which mode is highly symmetric? Mode #4
5. One mode is known as the "umbrella" mode, which one is this? Mode #1
6. How many bands would you expect to see in an experimental spectrum of gaseous ammonia? 3
Charge analysis
Charge on the N-atom: -1.125
Charge on the H-atoms: 0.375
A negative and positive charge of the N-atom and H-atom is expected respectively. This is because nitrogen is more electronegative than hydrogen.
H2 molecule
Optimisation of the molecule
Molecule name: H2
Calculation method: RB3LYP
Basis set: 6-31G(d.p)
Final energy E(RB3LYP): -1.17853936au
RMS gradient: 0.00000017au
Point group: C1
Bond distance: 0.74279
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
test molecule |
The optimisation file is linked to here.
Vibrations of the molecule
Frequency: 4465.68
N2 molecule
Optimisation of the molecule
Molecule name: N2
Calculation method: RB3LYP
Basis set: 6-31G(d.p)
Final energy E(RB3LYP): -109.52412868au
RMS gradient: 0.00000060au
Point group: C1
Bond distance: 1.10550
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
test molecule |
The optimisation file is linked to here.
Vibrations of the molecule
Frequency: 2457.33
Reaction energies
E(NH3)= -56.55776873au
2*E(NH3)= -113.1155375au
E(N2)= -109.52412868au
E(H2)= -1.17853936au
3*E(H2)= -3.53561808au
ΔE=2*E(NH3)-[E(N2)+3*E(H2)]= -0.05579074au = -146.4785879kJ/mol
The ammonia product is more stable because the energy required for conversion is negative, i.e. the energy of the ammonia product is lower than the total energy of the gaseous reactants.
Project molecule: F2
Optimisation of the molecule
Molecule name: F2
Calculation method: RB3LYP
Basis set: 6-31G(d.p)
Final energy E(RB3LYP): -199.49825218au
RMS gradient: 0.00007365au
Point group: C1
Bond distance: 1.40281
Item Value Threshold Converged? Maximum Force 0.000128 0.000450 YES RMS Force 0.000128 0.000300 YES Maximum Displacement 0.000156 0.001800 YES RMS Displacement 0.000221 0.001200 YES
test molecule |
The optimisation file is linked to here.
Vibrations of the molecule
Frequency: 1065.09
Charge analysis
There is no charge within the molecule because both of the atoms are F-atoms and there is no electronegativity difference between them.
Molecular orbitals
This is the first MOs, formed from the two 1s AOs of the F-atoms. The energy level is -24.79730au, which is much deeper comparing to the later MOs which are formed by the valence shell AOs. It can be seen that the orbitals is hardly overlapping, stating how it is not very involved in the chemical bonding between the F-atoms.
Moving on to the σ2s bonding orbital, which are formed from the 2s AOs of the F-atoms. The highly overlapping orbitals are almost shown as one surface only. They are of a much higher energy than the first two MOs where the energy level is -1.33659au. As these are formed from the valence shell AOs, they are highly involved in the chemical bonding.
The above 2 images shows the two σ2pz bonding and anti-bonding orbitals. The energy levels are -0.58753au and -0.12679au respectively. They are formed from the 2p orbitals of the F-atoms which lie along the same orientation as the F-F bond. Thus, it is a sigma MO. Due to the large energy gap between the 2s and 2p AOs, there is no mixing between the 2s and 2p orbitals and thus, the MOs do not give a distorted shape like those in N2. As the bonding orbital is occupied while the anti-bonding orbital is empty, these 2 electrons in the bonding orbital are the bonding electrons in F2.
The above 2 images shows the two π2p bonding and anti-bonding orbitals. The energy levels are -0.52332au and -0.39190au respectively. There are another 2 degenerate MOs because they are all formed from the 2px and 2py AOs of the F-atoms. They are perpendicular to the F-F bond and are called as pi MOs. As they are both occupied, the electrons in these MOs act as the non-bonding electrons. As a result, the fluorine molecule is only single bonded, which is contributed by the bonding electrons in the σ2pz bonding orbitals.