When applying energy to dihydrogen, a molecular electronic transition takes place when one electron in the bonding MO is promoted to the antibonding MO. This MO diagram also helps explain how a bond breaks. The bond order for dihydrogen is (2-0)/2 = 1. For bonding to exist the bond order defined as: The reduction in energy of these electrons is the driving force for chemical bond formation. The electrons in the bond MO are called bonding electrons and any electrons in the antibonding orbital would be called antibonding electrons. This MO is called the Highest Occupied Molecular Orbital or HOMO which makes the other orbital the Lowest Unoccupied Molecular Orbital or LUMO. Hund's rule states that when there are several MO's with equal energy the electrons fill one MO at a time.Īpplication of these rules for dihydrogen results in having both electrons in the bonding MO.The Pauli exclusion principle states that the maximum number of electrons occupying an orbital is two having opposite spins.The Aufbau principle states that orbitals are filled starting with the lowest energy.With the case of dihydrogen at hand two electrons have to be distributed over a bonding orbital and an anti-bonding orbital. The next step in constructing a MO diagram is filling the molecular orbitals with electrons. Like the bonding orbital this orbital is symmetrical but differentiated from it by an asterisk σ * bond In this anti-bonding MO with energy much higher than the original AO's the electrons are located in lobes pointing away from the central axis. The two hydrogen atoms can also interact with each other with their 1s orbitals out-of-phase which leads to destructive cancellation and no electron density between the two nuclei depicted by the so-called nodal plane as the vertical dashed line. The orbital is symmetrical with respect to rotation around the molecular axis (no change) and therefore also called a sigma bond (σ-bond). This MO is called the bonding orbital and its energy is lower than that of the original atomic orbitals. Then two same-sign orbitals have a constructive overlap forming a molecular orbital with the bulk of electron density located between the two nuclei. The sign of the phase itself does not have physical meaning except when mixing orbitals to form molecular orbitals. In graphical representations, the orbital phase is depicted either by a plus or minus sign (confusing because there is no relationship to electrical charge) or simply by shading. The phase of an orbital is a direct consequence of the wave-like properties of electrons. The two AO's can overlap in two ways depending on their phase relationship.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |