Purdue Chem 115 - Final Exam Latest Update Graded A

Purdue Chem 115 - Final Exam Latest Update Graded A Valence Bond Theory A model that attempts to reconcile the shapes of molecules with those of atomic orbitals through the concepts of orbital overlap and hybridization (429). hybridization a postulated process of orbital mixing to form hybrid orbitals (430). hybrid orbitals an atomic orbital postulated to form during binding by the mathematical mixing of specific combinations of nonequivalent orbitals on a given atom (430). sp hybrid orbital an orbital formed by the mixing of one s and one p orbital of a central atom (430). sp2 hybrid orbital an orbital formed by the mixing of one s and two p orbitals of a central atom (432). sp3 hybrid orbital an orbital formed by the mixing of one s and three p orbitals of a central atom (432). sp3d hybrid orbitals an orbital formed by the mixing of one s, three p, and one d orbital of a central atom (433). sp3d2 hybrid orbital an orbital formed by the mixing of one s, three p, and two d orbitals of a central atom (434). How to determine hybrid orbitals from molecular formula 1. take molecular formula, 2. create lewis structure, 3. determine molecular shape and electron group arrangement, 4. determine hybrid orbitals (434) - two helpful charts at bottom of page. sigma bond a type of covalent bond that arises through end-to-end orbital overlap and has most of its electron density along an imaginary line joining the nuclei (437). pi bond a covalent bond formed by sideways overlap of two atomic orbitals that has two regions of electron density, one above and one below the internuclear axis (437). What are the major principles of the Valence Bond theory? 1. a covalent bond forms when orbitals of two atoms overlap and a pair of electrons occupy that overlap region. 2. there are opposing spins of the electron pair. 3. there is a max. overlap of bonding orbitals (greater overlap = closer nuclei to electrons/stronger bond) What are features of hybrid orbitals? 1. the number of orbitals equals the number of atomic orbitals mixed, 2. the type of orbitals varies, 3. the shape and orientation of a hybrid orbital maximizes its overlap with the orbital of the other atom in the bond. Why is rotation about the bond axis restricted in molecules containing a pi bond? (i.e. either a double/triple bond) a pi bond restricts rotation because the p orbitals must be parallel to each other to overlap most effectively. What are the main differences between molecular mechanics, semi-empirical and Ab Initio computational models? 1. Molecular mechanics is used when a molecule is too big to effectively use the semi-empirical method. 2. Semi-empirical calculations can be done much faster than Ab Initio calculations, but results can be erratic. 3. Ab Initio gives very good qualitative results and they grow more accurate as size of molecule decreases. What are the major benefits/goals of computational chemistry? 1. Computational chemistry tools can be used to investigate a much wider variety of chemical species than are normally accessible to the experimental chemist. 2. is also allows chemists to think more clearly about issues that are really central to chemistry - structure, stability, and reactivity - than would be possible without the use of a computer. 3. g