Not successful in describing the excited states of molecules does not explain the existence of odd electron species also does not explain why o 2 is paramagnetic extends quantum theory and states that electrons spread throughout the molecule. The main purpose of this proposal was to explain the formation of chemical bonds and and to explain behaviour of molecules like their relative bond strength, paramagnetic and diamagnetic nature, stability etc. So, a diamagnetic substance is not attracted to a magnetic field. This site is like a library, you could find million. 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. Frontier molecular orbitals homo and lumo it makes sense. Chapter 5 molecular orbitals molecular orbital theory uses group theory to describe the bonding in molecules. Orbital 1s 2s 2p 2p 2p n 3 3 3 3 3 3333 l 0 1 1 1 2 2222 ml 0 10 1 2 10 1 2 orbital 3s 3p3p 3p 3d3d 3d3d 3d an introduction to molecular orbital theory lecture 2 representing atomic orbitals the schrodinger equation and wavefunctions.
These are often divided into three types, bonding, antibonding, and nonbonding. Using the molecular orbital model, select which kind of magnetism will be displayed by the following diatomic molecules or ions. Newest molecularorbitaltheory questions chemistry stack. In 1952, kenichi fukui published a paper in the journal of chemical physics titled a molecular theory of reactivity in aromatic hydrocarbons. Few theories have had the impact that molecular orbital. Electrons are located in discrete pairs between specific atoms. The molecular hamiltonian, simplified notation, bornoppenheimer mathematics, the variational theorem. Chart and diagram slides for powerpoint beautifully designed chart and diagram s for powerpoint with visually stunning graphics and animation effects. It is taught in various guises at all levels from introductory firstyear to.
A free powerpoint ppt presentation displayed as a flash slide show on id. Worlds best powerpoint templates crystalgraphics offers more powerpoint templates than anyone else in the world, with over 4 million to choose from. Crystal field theory only includes ionic interactions in the solid state mo theory developed and applied only to nonmetal compounds ligand field theory combines both for transition metal coordination compounds mos for oh complexes donor atom atom in the ligand with a porbital or hybrid orbital directly approaching the metal ion to form a. Molecular orbital mo theory uses a linear combination of atomic orbitals lcao to represent molecular orbitals resulting from bonds between atoms. The linear combination of two s orbitals overlaps to.
Chemists use such functions to predict or explain chemical and physical properties. Similar to an atomic orbital, a schrodinger equation, which describes the behavior of an electron, can be constructed for a molecular orbital as well. Introduction to hartree fockmolecular orbital theory pdf presentation 25p this note covers the following topics. Mmoolleeccuullaarr oorrbbiittaallss aann aapppprrooaacchh ttoo bboonnddiinngg iinn wwhhiicchh oorrbbiittaallss eennccoommppaassss tthhee eennttiirree mmoolleeccuullee, rraatthheerr tthhaann. In this chapter we shall apply molecular orbital theory to a wide variety of compounds in order to show that it may be used as a quite general means of description. Huckel molecular orbital hmo theory a simple quantum mechanical concept that gives important insight into the properties of large molecules why hmo theory the first mo theory that could be applied to large molecules. It represents an application of molecular orbital theory to transition metal. A crash course on molecular orbital theory for students of chem 332 mike evans introduction each semester in chem 332, we hold an outofclass workshop at the beginning of the semester addressing concepts from chem 232 that students will need to know for the second semester of organic chemistry. The second way that two atomic orbitals interact is outofphase. In addition to providing a unified explanation of diverse aspects of chemical reactivity and selectivity, it agrees with the predictions of the woodwardhoffmann orbital. They were designed primarily for advancedundergraduate and firstyear graduate students as an introduction to molecular orbital theory. Molecular orbital theory mo theory of bonding previous theories do not explain all aspects of bonding.
In molecular orbital theory the symmetry properties and relative energies of atomic orbitals determine how. Since orbitals are wave functions, they can combine either constructively forming a bonding molecular orbital, or destructively forming an antibonding molecular orbital. In some way, because of the paramagnetic character, we have a situation wich cannot be. Molecular orbital theory is more powerful than valencebond theory because the orbitals reflect the geometry of the molecule to which they are applied.
Sep 27, 2015 molecular orbital mo theory tells you that any linear combination of atomic orbitals aos gives you the corresponding molecular orbital s. So, molecular orbital theory, on the other hand, is based on quantum mechanics. The second pair of electrons is shared in a pi bond that results from sidetoside overlap of the unhybridized p orbital on carbon and the corresponding p orbital on oxygen figure on the right below. Which one of these explains the paramagnetism of o2. While the electrons in an atom or molecule are all paired, the magnetic fields caused by electron spin and orbital angular momentum tend to cancel each other, resulting in diamagnetism. The subdivisions of the chapter are thus more a matter of convenience than a reflection of changes in the principle of the approach. Day 8 molecular orbital theory part 3 1 inorganic chemistry with doc m. How would valence bond theory describe the hybridization of the sulfur atom. The scf procedure allows satisfactory predictions for these properties compared with experimental results.
Ppt molecular orbital theory powerpoint presentation free. In the diatomic species, in constructing the molecular orbital diagram, we simply show the energies of the atomic orbitals of the two species on either side of the diagram and the energies of the molecular orbitals in the center. Molecular orbital theory slides molecular orbital theory. Though widely criticized at the time, he later shared the nobel prize in chemistry with roald hoffmann for his work on reaction mechanisms. Molecularorbitaltheory amoreaccurate theory thanvalencebond theory ismolecular orbital. The basic idea of the theory is that atomic orbitals of the individual atoms combine to form molecular. An introduction to molecular orbital theorymolecular orbital theory lecture 1 the bohr model prof g.
A bonding orbital concentrates electron density in the region between a given pair of atoms, so that its electron density will tend to attract each of the two nuclei. These molecules serve to illustrate the concept of ligand group orbitals lgos and subsequent construction of mo energy diagrams on. In chemistry, a molecular orbital or mo explains what happens to electrons when atoms join together in a molecule. Use of molecular orbital mo theory allows for an understanding of the observed properties shape, reactivity of molecules. Read online an introduction to molecular orbital theory. Linear combinations of atomic orbitals, the sums and differences of the atomic wavefunctions provide approximate solutions to the molecular schrodinger equations.
Molecular orbital theory uses group theory to describe the bonding in molecules. For example, the functions can tell the probability of finding an electron in any specific region. This could be simply donating electron density to form a bond act as a lewis base or it. For quantitative predictions of binding energies and geometrical parameters. In molecular orbital theory, bond order is also defined as the difference, divided by two, between the number of bonding and antibonding electrons. Molecular orbitals of complexes group theory is also used to construct molecular orbital diagrams for the complexes of metal atoms or ions. This theory was proposed by hund and mulliken in 1932. The power of the mo theory is not in visualizing the molecule and its bonds, but in the ability to predict whether a molecule will exist and explain its characteristics for every combination of atomic orbitals, there are two possible molecular orbitals. Orbitals an approach to bonding in which orbitals encompass the entire molecule, rather than being localized between atoms molecular orbitals molecular orbitals result from the combination of atomic orbitals. These notes are based on lectures on molecular orbital theory that we have presented at the university of copenhagen and columbia university. We have a picture of atoms with an electronic structure described by orbitals. This is a question for my chemistry final and i have looked everywhere but cant find. Guides the reader through a progression from the most elementary ideas of molecular orbital theory to an understanding of the electronic structure, geometry, and reactivity of the larger molecules.
Molecular orbital simple english wikipedia, the free. Stability and lability substitution reactions electron transfer reactions descriptive chemistry of tms. All orbitals are occupied by pairs of electrons not paramagnetic 1. Electron configuration of transition metals crystal field theory valence bond theory simple molecular orbital theory electronic spectra and magnetism kinetics and mechanisms of inorganic reactions. If we start at the nucleus and move away, the 1s orbital always retains the same sign. Molecular orbital theory for polyatomic molecules every. A mo is a mathematical function which describes the wavelike behaviour of an electron in a molecule. Explaining its principles, sigma and pi bonds, bond order, and molecular stability. Heteronuclear molecules georgia institute of technology. In chemistry, frontier molecular orbital theory is an application of mo theory describing homolumo interactions. A qualitative approach based on symmetry and overlap ideas is the focus of the presentation.
This is mainly due to the fact, that occupied orbitals behave differently than unoccupied orbitals. Ppt molecular orbital theory powerpoint presentation. From these observations, frontier molecular orbital fmo theory simplifies prediction of reactivity to analysis of the interaction between the more energetically matched homolumo pairing of the two reactants. The 10step approach to making mo diagrams via symmetry considerations 3. A brief introduction to molecular orbital theory of simple. Introduction to hartree fockmolecular orbital theory pdf. Use hybridization to describe molecular geometries.
Symmetry adapted linear combinations salc of bonding group atomic orbitals 2. Molecular orbital theory we would like a theory of bonding that can be visualized and is at least semiquantitative. Download an introduction to molecular orbital theory. The figure below is a representation of what type of orbital. It is apparent that the molecular orbital theory is a very useful method of classifying the ground and excited states. Hoffmans work focused on creating a set of four pericyclic reactions in organic chemistry, based on. Nov 24, 2009 we use your linkedin profile and activity data to personalize ads and to show you more relevant ads. A crash course on molecular orbital theory for students of. Molecular orbital theory lecture linkedin slideshare. These molecules serve to illustrate the concept of ligand group orbitals lgos and subsequent construction of mo energy diagrams on the basis of molecular symmetry. A molecular orbital diagram, or mo diagram, is a qualitative descriptive tool explaining chemical bonding in molecules in terms of molecular orbital theory in. Winner of the standing ovation award for best powerpoint templates from presentations magazine. And specifically, mo theory is the quantum mechanical description of wave functions within molecules.
Bond order is also an index of bond strength, and it is used extensively in valence bond theory. Chemistry molecular orbital theorey what are homodiatomic. Molecularorbitaltheory amoreaccuratetheorythanvalencebondtheoryismolecular orbital. The tag should be applied to all questions related to mo theory, from questions about the qualitative use of the theory to questions about the underlying quantum mechanics and applications in computational chemistry. There are three main requirements for atomic orbital combinations to be suitable as approximate molecular orbitals. Molecular orbital theory for polyatomic molecules every science. A simple, fourstep method for better introducing undergraduate students to the fundamentals of molecular orbital mo theory of the polyatomic molecules h 2 o, nh 3, bh 3 and sih 4 using group theory is reported. So, saying wave functions within molecules might sound a little confusing, but remember we spent a lot of time talking about wave functions within atoms, and we. In molecularorbitaltheory,weimaginethat electronic. The molecular orbital formed is symmetrical about the axis of the bond. Atomic orbital energy correlates with electronegativity, as electronegative atoms hold electrons more tightly, lowering their energies.
All books are in clear copy here, and all files are secure so dont worry about it. For example, to give you a glimpse at where we are headed, the following are orbital diagrams for. In mo theory, molecular orbitals form by the overlap of atomic orbitals. Molecular orbital theory california institute of technology. Molecular orbital theory was seen as a competitor to valence bond theory in the 1930s, before it was realized that the two methods are closely related and that when extended they become equivalent. Now that we have discussed hybrid orbital theory and resonance theory, lets finally turn our attention to molecular orbital mo theory. Our new crystalgraphics chart and diagram slides for powerpoint is a collection of over impressively designed datadriven chart and editable diagram s guaranteed to impress any audience. Lines are drawn to connect the molecular orbitals with their basis. Electrons are located in the molecule, not held in. Linear combination literally means moving the atomic orbitals towards each other linearly through space until they overlap. It makes sense that the homo and lumo are the orbitals most likely to be involved in chemical reactivity. 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. Whilst we can imagine the hybrid orbitals of valence bond.
Chemistry 332 basic inorganic chemistry ii ualberta. But this power carries a significant cost in terms of the ease with which the model can be visualized. Molecular orbitallinear combination of atomic orbitals lewis dot structures dont work for excited states. Mo modeling is only valid when the atomic orbitals have comparable energy. The symmetry combinations of the atomic orbitals on the ligands are determined, and then matched with appropriate atomic orbitals on the central metal. Molecular orbital theory for o 2 o o lewis diagram predicts sp2 hybridization on o atoms sp 2 bp z sp2 sp2 bp sp sp sp2. Atomic orbital models molecular orbital and valence bond calculations of the welectron energies of unsaturated molecules custom arily start with models in which appropriate atomic orbitals are assigned to each nucleus to provide a framework for notions of the binding electrons. A theory that can be implemented without the aid of a computer. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
General chemistry intermolecular forces molecular orbital theory part 2view the complete course. Hence, each bonding orbital is described by a wavefunction with the form this picture of the formation of the molecular orbitals. In water, there is sp 3 hybridization, forming two bonding orbitals, where the hoh bonding angle is close to the tetrahedral angle of 109. Theyll give your presentations a professional, memorable appearance the kind of sophisticated look that todays audiences expect. Structural applications of molecular orbital theory.