6/9/2023 0 Comments Homo lumo diagramIn a redox reaction, the oxidant has a low LUMO, and the reductant has a high HOMO, but this time the oxidant LUMO is lower than the reductant HOMO, so that the electrons in the reductant HOMO move completely to the oxidant LUMO. This creates a bond between the acid and base. A low LUMO usually means an empty valence orbital, like on B or on a cation.) We can make a bonding and anti-bonding combination of the base HOMO and acid LUMO, and that will stabilize the electrons from the base's HOMO, lowering the total energy. (A lone pair in MO theory is an electron pair in a non-bonding MO. What this really means is that the base has a HOMO that is pretty high-energy (a lone pair), and the acid has a LUMO that is pretty low energy. In a Lewis acid/base reaction, an electron pair from the base is shared with the acid. Earlier, we said that most reactions can be called either Lewis acid/base or redox. LUMO is Lowest Unoccupied MO, the lowest-energy MO that doesn't have any electrons in it.įrontier MOs are very important for reactivity. HOMO is Highest Occupied MO, the highest-energy MO that has electrons in it. The frontier MOs are called the HOMO and the LUMO. In this case, we are interested in the MOs at the border between occupied and empty. Distinguish and describe the significance of frontier MOsįrontier means a border area, between two things (often, between 2 countries).Till then ,īe a perpetua l student of life and keep learning.\) Now that we know how to construct the MO diagram, we shall study the symmetry of MOs in the next post. The electronic configuration of H 2 molecule can be represented as – (σ 2s ) 2 This configuration gives us a clear picture of the way electrons occupy the MOs. Similarly, molecules have an electronic configuration too. We know that the electronic configuration of an atom tells us the whereabouts of an electron in it. Thus, there is a single bond between two H- atoms in an H 2 molecule. In the above figure, σ is HOMO, and σ* is LUMO. Thus, it is drawn in between the AOs of two atoms. Remember, the BMO is delocalized i.e it is spread on both the atoms and so the electrons are not on anyone atom anymore. So, the two electrons sit in the BMO(σ1s), as shown in the above figure. These two AOs form two orbitals –īonding orbital (σ) – This is drawn in the centre, between the two AOs and it lies below the two AOs of hydrogen.This is because it has lower energy than the two atomic orbitals.Īnti bonding orbital (σ*) – This orbital again lies in between the two AOs but it is higher in energy than the two AOs and so it lies above them.Īs we know, the electrons shall pair up and then occupy the MO with the least energy ( Aufbau principle), which is always the bonding MO. There is one electron each in the 1s AO of hydrogen atom. The atomic orbitals (AO) are drawn on the extreme right and extreme left of the MO diagram. Now let us begin by constructing a MO diagram for H 2 molecule. The energy difference between them is called HOMO-LUMO gap. The molecular orbital which is occupied by electrons and has the highest energy is called HIGHEST OCCUPIED MOLECULAR ORBITAL(HOMO) and the orbital with lowest energy which is vacant is termed as LOWEST UNOCCUPIED MOLECULAR ORBITAL(LUMO).Electrons get filled in MOs in accordance with Afbau principle -orbitals with lower energy get filled first.The Y-axis shows energy of the orbitals.The MOs are drawn between these two ends. The atomic orbitals are shown on the far left and far right of the diagram.However, before proceeding, we will study the rules of drawing a MO diagram. We begin with the simplest of all homonuclear diatomic molecules – The H 2 molecule. In this post, we shall begin by constructing MO diagrams for various molecules.
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