Question

what is basic pauchlete of melecular orbital theries

Answer 1

You probably know the general shape of the s (spherical), p (looks like two elongated balloons tied together), d (most of them look like four elongated balloons, except for the dz^2 orbital whichlooks like two with a donut surrounding thejunction), and thanks to David Trauffer above, the f orbitals. A long time ago, therewas much discussionabout how these atomic orbitals became bonding orbitals. I mean, there are no atomic orbitals that form a tetrahedron around an atom, so how do you explain the shapeof methane (CH4)? Worse, carbon shouldonly form two bonds because the 2s orbital is filled and there are only two electrons in the 2p orbitals. Then along came valence bond theory. This theory said that the atomic orbitals combined to form multiple equivalent orbitals. So, going back to methane, the 2s and the 2p orbitalscombined to form four hybrid orbitals (which were called sp^3 orbitals). Everyone nodded and went away happy.Then some chemists noticed that valence bond theory couldn't account for the bonding of aromatics,like benzene. All right, I am hugely simplifying here, but work with me, all right? Molecular orbital theory extends valence bond theory. (At first everyone thought that the two theories were incompatible, but then they figured out that for simple molecules the two theories were equivalent.) In molecular orbital theory the atomic orbitals of multiple atoms combine. In effect, the atomic orbitals are smeared out across the entire molecule. This allows us to account for the electrons in anaromatic ring, and, in fact, allows us to predict that an aromatic ring will be more stable than the equivalent structure with isolated pi bonds. Today, molecular orbital theory is the basis for a number of quantum mechanical calculations. These calculations assume the electron wave function is a Linear Combination of Atomic Orbitals. I hope this helps make the basic concept clear!