Note rule 2 that the antibonding mo is polarized in. In this theory, each molecule has a set of molecular orbitals. Using molecular orbital theory, we can rationalize why molecular hydrogen h 2 is an abundant molecule whereas molecular helium he 2 is not. Electrons may be considered either of particle or of wave nature. Symmetry adapted linear combinations, salcs topics. Robert mulliken introduced the term orbital in 1932 to describe a oneelectron orbital wave function. Tuesday, october 9, 2001 page 1 of 6 lecture notes j. An introduction to molecular orbital theorymolecular orbital theory. Hybridization and molecular orbital mo theory chapter 10 historical models valence bond theory vb a molecule arises from interaction of complete atoms, bound together through localized overlap of valenceshell atomic orbitals which retain their original character. However, there are 2 nuclei so it becomes a 3particle problem. These combination or interaction of atomic orbitals can be bonding or anti bonding. Chemists use such functions to predict or explain chemical and physical properties. Day 8 molecular orbital theory part 3 1 inorganic chemistry with doc m.
For example, to give you a glimpse at where we are headed, the following are orbital diagrams for. Therefore, an electron in an atom may be described as occupying an atomic orbital, or by a wave function. The papers treat a substantial number of the important molecular geometries. 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. Frontier molecular orbital fmo theory allows a chemist to make predictions about a reaction by knowing. Molecular orbital theory explains how this is possible. 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. It is apparent that the molecular orbital theory is a very useful method of classifying the ground and excited states. Introduction to hartreefock molecular orbital theory. 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. Mmoolleeccuullaarr oorrbbiittaallss aann aapppprrooaacchh ttoo bboonnddiinngg iinn wwhhiicchh oorrbbiittaallss eennccoommppaassss tthhee eennttiirree mmoolleeccuullee, rraatthheerr tthhaann.
Two electrons with paired spins may be symbolized as fc. Learn vocabulary, terms, and more with flashcards, games, and other study tools. We use molecular orbital mo theory to actually explain chemical bonding. For any two sets of p orbitals on two different atoms, corresponding orbitals such as p x orbitals can overlap headon. Chapter 5 molecular orbitals molecular orbital theory uses group theory to describe the bonding in molecules. Chemistry 310 lecture notes mo theory 3 for the simple case where. However,elementsofmolecularorbitaltheory arenecessaryformanydiscussionsofchemicalandphysicalproperdesandsowillwill discusssomebasicprincipleshere. Symmetry adapted linear combinations salc of bonding group atomic orbitals 2. Two or more atoms combine together to form molecular orbitals. In chemistry, a molecular orbital or mo explains what happens to electrons when atoms join together in a molecule. They were designed primarily for advancedundergraduate and firstyear graduate students as an introduction to molecular orbital theory.
Molecular orbital theory for example, when two hydrogen atoms bond, a. In molecularorbitaltheory,weimaginethat electronic. The new orbitals thus formed are called molecular orbitals. If the overlap integral between two orbitals centered on different atoms is zero, then there is no interaction between them. The symbols fi or bt represent two electrons that may not go together into a single orbital. Express the electronic wavefunction as a single slater determinant 3. Electrons in a molecule are said to occupy molecular orbitals.
If the remaining p orbitals overlap py with p y and p z with p z, they must do so sideways, or sideon, forming pi molecular. In mo theory, molecular orbitals form by the overlap of atomic orbitals. If an orbital has s 0 with all other orbitals in the molecule, then it is a 100% nonbonding orbital. S 0 if orbitals have different irreducible representations. Atomic orbital energy correlates with electronegativity, as electronegative atoms hold electrons more tightly, lowering their energies. Mo theory basics whilstwecanimaginethehybrid orbitals ofvalencebond theory veryeasily,weneed computerstovisualisemolecularorbitals. Mulliken in 1932 as an abbreviation for oneelectron orbital wave function. A molecular orbital is an orbital or wave function of a molecules electron.
Lecture b6 molecular orbital theory sometimes its good to be alone. Such a pair of electrons can go into a single orbital. When two atomic orbitals overlap or combine,they lose their identity and form new orbitals. Note that the ao basis determines the dimension of our mo vector and.
These are often divided into three types, bonding, antibonding, and nonbonding. The figure below is a representation of what type of orbital. The reader should be able to follow the discussions after reading through the lecture notes. Mo theory is complex, so we will look only at the simple case of diatomic molecules such as h2, o2, n2, co. Note that the 1sigma and 2sigma molecular orbitals of hydrogen fluoride are mostly derived from the fluorine 2s and 2p atomic orbitals respectively. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. One can mention numerous examples such as the role of hbonding in water 1, proton transfer processes 2,3, enzymatic catalysis 4,5, protein folding 6, and also its important role in other fields. Molecular orbital theory mo theory provides an explanation of chemical bonding that accounts for the paramagnetism of the oxygen molecule.
Valence bond and molecular orbital theories lecture notes may 4, 2006 prof. Several reprints of papers on molecular orbital theory are included in the back of the book. How would valence bond theory describe the hybridization of the sulfur atom. The function may be used to calculate the probability of finding an electron within a specified space or to predict the molecules chemical and physical properties. A bonding orbital is formed by the interaction of two atomic orbitals from the same phase whereas anti bonding orbital is. The bond that is formed is a molecular orbital and to this point, we have simply called them. Atoms, molecules, and ions, electronic structure and periodic properties of elements, chemical bonding and molecular. 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. Molecular orbital theory lecture linkedin slideshare. For c, n, and o hybridization means the 2s atomic orbital is combined with one, two, or all three 2p atomic orbitals. Molecular orbital theory mot, chemistry study material. Molecular orbital theory is a method for determining molecular structure. 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. Molecular orbital simple english wikipedia, the free.
The molecular orbital theory does a good job of predicting elctronic spectra and. It uses 3d pictorial presentations of molecular orbitals to elucidate organic reaction mechanisms such as those found in pericyclic chemistry. We use your linkedin profile and activity data to personalize ads and to show you more relevant ads. 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. Hydrogen bonding hbonding is an essential interaction in nature and plays a crucial role in physical, chemical and biological processes.
Consequently, the ability to understand hbonding is of great. 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. It describes electrons as moving under the influence of the nucleus and not assigned to specific bonds. In the application of molecular orbital theory to calculations of chemical binding.
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. Energy level diagram learnnext offers animated video lessons with neatly explained examples, study material, free ncert solutions, exercises and tests. Molecular orbital mo theory uses a linear combination of atomic orbitals lcao to represent molecular orbitals resulting from bonds between atoms. The following slide illustrates the relative energies of the molecular orbitals compared to the original atomic orbitals. Molecular orbital theory predicts the placement of electrons in a molecule. The 10step approach to making mo diagrams via symmetry considerations 3. These notes are based on lectures on molecular orbital theory that we.
In chemistry, a molecular orbital mo is a mathematical function describing the wavelike behavior of an electron in a molecule. Section 2 simple molecular orbital theory in this section, the conceptual framework of molecular orbital theory is developed. In molecular orbital theory the symmetry properties and relative energies of atomic orbitals determine how. Mo theory is complex, so we will look only at the simple case of diatomic molecules such as h 2, o 2, n 2, co, and hf. Molecular orbital analysis of the hydrogen bonded water dimer. These notes are based on lectures on molecular orbital theory that we have presented at the university of copenhagen and columbia university. Molecularorbitaltheory amoreaccuratetheorythanvalencebondtheoryismolecular orbital. The next slide illustrates the relative energies of these molecular orbitals for homonuclear diatomic molecules composed of 2nd period elements. Introduction to molecular orbital theory this collection of web documents can be used as a backup to henry rzepas online pericyclic chemistry course. Molecular orbital theory an introductory lecture mip en citricos pdf note and reprint volume. Bond order can be calculated by considering all electrons or only.
Valence shell electron pair repulsion theory vsepr predicts. Orbital theory textbook ch 9 intermolecular forces textbook ch 11 imf notes were posted 1st quarter so check to see if you have already printed them. 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. A mo is a mathematical function which describes the wavelike behaviour of an electron in a molecule. Mo modeling is only valid when the atomic orbitals have comparable energy.
If you want to power your starship with dilithium li 2 crystals, you should watch this lecture. Recall that bonds are formed from overlap of electron cloud density from two atomic orbitals. For example, the functions can tell the probability of finding an electron in any specific region. In molecular orbital theory, we calculate bond orders by assuming that. Applications are presented and problems are given and solved within qualitative and semiempirical models of electronic structure. 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. Symmetry properties and degeneracy of orbitals and bonds can be.