There are two ways to predict the properties of a resonance hybrid. Now that you can see how "superposition of wave functions" (i.e., resonance) works, I'll explain why it is important to use this approach when predicting molecular properties. The standard resonance drawing is equivalent to the more convoluted mathematical treatment. When this delocalized orbital is occupied, it simultaneously creates three partial, identical HH bonds. Instead of combining orbitals from two atoms, like a normal bond orbital, BO(hybrid) combines orbitals from three atoms. Notice that the hybrid's wave function looks like a bond orbital, except that it is delocalized. If we substitute the definitions of each BO into this formula, we can get a formula for BO(hybrid) in terms of H 1s orbitals: Next, we construct a superposition of these wave functions. If we write these bond orbitals as bonding combinations of H 1s orbitals, and label the 1s orbitals, we can see the differences between these wave functions: In wave function language, each form corresponds to a doubly-occupied HH bond orbital ( BO). Since the ion contains only two electrons, it must be a resonance hybrid:Įach resonance form contains one electron pair, a bond pair between two H. This ion is shaped like an equilateral triangle, which indicates three identical HH bonds. I'll illustrate this procedure for H 3 +. Then, we superposition the wave functions to generate the resonance hybrid's wave function. First, we translate each form into its corresponding wave function. The same kind of "Lewis structure = wave function" idea can be applied to resonance forms (which is what Pauling intended). If we know how to draw the Lewis structure, we know how to write the wave function, and vice versa. As the following diagram shows, every electron pair in the Lewis structure corresponds to a specific doubly-occupied orbital in the wave function. To see how one translates a Lewis structure into a wave function, consider a simple molecule like water. And this translation is a necessary step when one uses resonance theory. A Lewis structure can, in fact, be translated directly into a specific wave function. Obviously, Lewis structures and wave functions both describe electrons, but the similarity goes deeper. A wave function is a mathematical formula consisting of orbitals. Lewis structure as a wave function, and how this affects the prediction of molecular properties.Ī Lewis structure is a drawing consisting of symbols for bond pairs and lone In this essay, I try to explain how one can view a The distinction between wave function and Lewis structure is a subtle one, and this probably explains why the modern error has been perpetuated for so long. Unfortunately, this detail has been lost in the intervening decades, and modern chemists incorrectly treat "resonance" as the superposition of Lewis structures (resonance forms). When Linus Pauling developed resonance theory, he defined "resonance" as the superposition of wave functions. I wrote it mainly to scratch an itch that has been In any case, youĭon't have to read this essay in order to use resonance The information is too difficult or you don't really need to know This essay contains information that I have neverįound in any organic chemistry textbook.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |