Valence bond and molecular orbital theories lecture notes may 4, 2006 prof. Molecular orbitals one approach to understanding the electronic structure of molecules is called molecular orbital theory. Molecular orbital theory the goal of molecular orbital theory is to describe molecules in a similar way to how we describe atoms, that is, in terms of orbitals, orbital diagrams, and electron configurations. Chemistry 310 lecture notes mo theory 1 molecular orbital theory valence bond theory gave us a qualitative picture of chemical bonding. Molecular orbital theory lecture notes, notes, pdf free download, engineering notes, university notes, best pdf notes, semester, sem, year, for all, study material. Valence bond theory of covalent bonding for elements more complicated than hydrogen, it is helpful to combine hybridize the valence atomic orbitals on a given atom before looking for overlap with orbitals from other atoms.
Sevian agenda zvalence bond theory zbonds are formed by overlap of atomic orbitals zbefore atoms bond, their atomic orbitals can hybridize to prepare for bonding zmolecular geometry arises from hybridization of atomic orbitals z. The molecular orbital theory describes how the orbital shapes combine when atoms combine into molecules. Molecular orbital theory mo a molecule is formed by the overlap of atomic orbitals to form molecular orbitals, electrons are then distributed into mos. Molecular orbital theory for example, when two hydrogen atoms bond, a. This video is part of a 23lecture undergraduatelevel course titled. Useful for predicting shapes of molecules, bond strengths, etc.
Molecular orbitallinear combination of atomic orbitals lewis dot structures dont work for excited states. Lecture b7 molecular orbital theory, part 2 different is interesting. Why do some atoms readily form bonds with each other and other atoms dont. Introduction to molecular orbital theory 1 introduction to molecular orbital theory. To begin with, we are going to treat what is absolutely the simplest molecule we can imagine. Valence shell electron pair repulsion theory vsepr predicts molecular shapes based on valence electrons, lewis dot structures and electron repulsions. General chemistry intermolecular forces molecular orbital theory part 2. We want to see what wavefunctions look like on molecules, not just atoms. If you want to power your starship with dilithium li 2 crystals, you should watch this lecture. In molecularorbitaltheory,weimaginethat electronic. You will be redirected to the full text document in the repository in a few seconds, if not click here.
N molecular orbitals can be constructed by n atomic orbitals. The molecular orbital theory does a good job of predicting elctronic spectra and. General chemistry intermolecular forces molecular orbital theory part 1 view the complete course. Explore prime new internship new upload login register. Molecularorbitaltheory amoreaccuratetheorythanvalencebondtheoryismolecular orbital. Ppt introduction to molecular orbital theory powerpoint. It also explains the bonding in a number of other molecules, such as violations of the octet rule and more molecules with more complicated bonding beyond the scope of this text that are difficult to describe with lewis structures. Hartreefock selfconsistentfield theory outline of today s lecture postulates in quantum mechanics schr dinger equation powerpoint ppt presentation. Introduction to hartreefock molecular orbital theory. The simplest molecule is hydrogen, which can be considered to be made up of 2 divide protons and electrons. Molecular orbital theory mulliken delocalized orbital approach unoccupied orbital spectroscopic properties ionization, excited states chem 104a, uc, berkeley valence bond theory valence bond theory vbt is a localized quantum mechanical approach to describe the bonding in molecules. Molecular orbital theory fsc part 1 inter chemistry. Valence bond theory generally fails to explain the bonding in simple. A more advanced description of orbitals in molecules.
Lecture b6 molecular orbital theory sometimes its good to be alone. This lecture note explains the following topics related to computational chemistry. Electrons may be considered either of particle or of wave nature. However, there are 2 nuclei so it becomes a 3particle problem. In order to determine the shape, the lewis diagram must be drawn first. General chemistry intermolecular forces molecular orbital theory part 1view the complete course. The vsepr theory is used to predict the shapes of molecules based on the repulsion of the bonding and nonbonding electrons in the molecule.
In molecular orbital theory, we calculate bond orders by assuming that. An introduction to molecular orbital theorymolecular orbital theory. It fails to describe some bonding situations accurately because it ignores the wave nature of the electrons. We use molecular orbital mo theory to actually explain chemical bonding. Mo theory assumes that the valence electrons of the atoms within a molecule become the valence electrons of the entire molecule. Because arguments based on atomic orbitals focus on the bonds formed between valence electrons on an atom, they are often said to involve a valencebond theory the valencebond model cant adequately explain the fact that some molecules contains two equivalent bonds with a bond order between that of a single bond and a double bond. Molecular orbital theory we use molecular orbital mo theory to actually explain chemical bonding. Therefore, an electron in an atom may be described as occupying an atomic orbital, or by a wave function. Using molecular orbital theory, we can rationalize why molecular hydrogen h 2 is an abundant molecule whereas molecular helium he 2 is not.
Molecular orbital theory, part 2 english uci chem 1a general chemistry winter 20 lec 15. This collection of web documents can be used as a backup to henry rzepas online pericyclic chemistry course. These lecture notes have been prepared to give an introduction into the foundations of atomic and molecular physics with an emphasis on the interaction of these. These notes are based on lectures on molecular orbital theory that we have presented at the university of copenhagen and columbia university. In atoms, electrons take up atomic orbitals, but in molecules they dwell in similar molecular orbitals that surround the molecule. Two or more atoms combine together to form molecular orbitals. Mmoolleeccuullaarr oorrbbiittaallss aann aapppprrooaacchh ttoo bboonnddiinngg iinn wwhhiicchh oorrbbiittaallss eennccoommppaassss tthhee eennttiirree mmoolleeccuullee, rraatthheerr tthhaann. Electrons in a molecule are said to occupy molecular orbitals. They were designed primarily for advancedundergraduate and firstyear graduate students as an introduction to molecular orbital theory. Homonuclear molecules with mos originating from s orbitals. Molecular orbital theory an introductory lecture mip en citricos pdf note and reprint volume. Chapter 5 molecular orbitals molecular orbital theory uses group theory to describe the bonding in molecules.
The shape is determined by the number of bonding and nonbonding electrons in the molecule. Here i informed you that what is molecular orbital theory in 3d. An introduction to molecular orbital theory 6 lecture course prof s. Your support will help mit opencourseware continue to offer high quality educational resources for free. Mo theory is superior to vsepr and vb which focus only on the central atom.
Tuesday, october 9, 2001 page 1 of 6 lecture notes j. Molecular orbital atomic orbitals linear combination of atomic orbitals lcao creates a. Express the electronic wavefunction as a single slater determinant 3. We use your linkedin profile and activity data to personalize ads and to show you more relevant ads. Molecular orbital theory mot, chemistry study material. Mo theory was originally called the hundmulliken theory. During the course of chemical reactions, the interaction of. Frontier molecular orbital fmo theory allows a chemist to make predictions about a reaction by. Molecular orbital theory mo theory provides an explanation of chemical bonding that accounts for the paramagnetism of the oxygen molecule.
The following slide illustrates the relative energies of the molecular orbitals compared to the original atomic orbitals. It uses 3d pictorial presentations of molecular orbitals to elucidate organic reaction mechanisms such as those found in pericyclic chemistry. And what we end up forming is a molecular orbital, because as we bring these two atomic orbitals close together, the part between them, that wave function, constructively interferes such that in our molecular orbital. It is apparent that the molecular orbital theory is a very useful method of classifying the ground and excited states. These lecture notes have been prepared to give an introduction into the foundations of atomic and molecular physics with an emphasis on the interaction of these atomic systems with light, and in more general, with electromagnetic fields. A brief introduction to molecular orbital theory of simple. These notes are based on lectures on molecular orbital theory that we. In this lecture we will understand how the molecular orbitals are formed from the.
A brief introduction to molecular orbital theory of simple polyatomic molecules for undergraduate chemistry students. In molecular orbital theory the symmetry properties and relative energies of atomic orbitals determine how. Molecularorbitaltheory amoreaccurate theory thanvalencebond theory ismolecular orbital. Solve for those orbitals which minimize the electronic energy variational method this winds up being mathematically equivalent to assuming each electron interacts only with the average. For example, to give you a glimpse at where we are headed, the following are orbital diagrams for. Molecular orbital theory predicts the placement of electrons in a molecule. Introduction to hartree fockmolecular orbital theory pdf. Molecular orbital theory 1 bond formation bonding between two 1s orbitals in h2 h2 versus he2 definition of bond order bond order number of bonding electrons number of antibonding electrons2 if atom b is more electronegative than atom a 1s 1s a b. Download englishus transcript pdf the following content is provided under a creative commons license. For c, n, and o hybridization means the 2s atomic orbital is combined with one, two, or all three 2p atomic orbitals.