Draw the molecular orbital diagrams of the N2 molecule in the ground state, and its next three excited states. There should be a total of four molecular orbital diagrams.
The Correct Answer and Explanation is:
The molecular orbital diagram for the N2 molecule in its ground state and excited states involves populating the molecular orbitals (MOs) according to the number of electrons and their respective energy levels. Here’s a step-by-step explanation:
Ground State of N2:
The nitrogen molecule (N2) has 14 electrons (7 from each nitrogen atom). The molecular orbitals are filled in the following order:
- σ(1s) and *σ(1s)**: These orbitals are filled first with two electrons in each.
- σ(2s) and *σ(2s)**: These orbitals are filled with two electrons in each.
- π(2px) and π(2py): These degenerate orbitals are filled with four electrons, two in each.
- σ(2pz): This orbital is filled with two electrons.
- π(2px)* and *π(2py)**: These are the anti-bonding orbitals, and they are unoccupied in the ground state.
- *σ(2pz)**: This anti-bonding orbital is also unoccupied in the ground state.
Thus, in the ground state, the electrons are placed in the lowest energy orbitals available, with the highest occupied molecular orbital (HOMO) being the σ(2pz) orbital.
Excited States of N2:
In each of the excited states, one or more electrons from lower-energy orbitals are promoted to higher-energy orbitals. We will look at the next three excited states:
- First Excited State: One electron is promoted from the σ(2pz) orbital to the π(2px)* or π(2py)* orbital.
- Second Excited State: Two electrons are promoted. One goes from the σ(2pz) to the π(2px)* orbital, and the other from π(2px) to *π(2px)**.
- Third Excited State: Three electrons are promoted. One goes from σ(2pz) to *π(2px), another from π(2px) to *π(2px), and one from π(2py) to *π(2py)**.
Each of these excited states has a higher energy than the previous one, as the electrons occupy higher energy anti-bonding orbitals.
In all four diagrams, the x-axis represents the molecular orbitals, from the lowest energy (at the bottom) to the highest energy (at the top). The y-axis represents the energy levels, and the number of electrons is indicated by arrows.
The excited states differ from the ground state in that they have electrons in higher anti-bonding orbitals, leading to a decrease in bond order and bond strength.
