Molecular Orbital Theory - Ppt Free Download EXCLUSIVE

Our teacher has experience as a researcher and professor but hasn't taught AP Chem many times. He uses Zumdahl's chemistry textbook, which goes into a lot of detail about molecular orbital theory and bonding and antibonding... I've been confused by it for the past few lectures and haven't been able to really understand it, which is making me worry a little bit.

The molecular orbital theory (often abbreviated to MOT) is a theory on chemical bonding developed at the beginning of the twentieth century by F. Hund and R. S. Mulliken to describe the structure and properties of different molecules. The valence-bond theory failed to adequately explain how certain molecules contain two or more equivalent bonds whose bond orders lie between that of a single bond and that of a double bond, such as the bonds in resonance-stabilised molecules. This is where the molecular orbital theory proved to be more powerful than the valence-bond theory (since the orbitals described by the MOT reflect the geometries of the molecules to which it is applied).

Molecular Orbital Theory - Ppt Free Download

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In simple terms, the molecular orbital theory states that each atom tends to combine together and form molecular orbitals. As a result of such an arrangement, electrons are found in various atomic orbitals, and they are usually associated with different nuclei. In short, an electron in a molecule can be present anywhere in the molecule.

Molecular orbitals can generally be expressed through a linear combination of atomic orbitals (abbreviated to LCAO). These LCAOs are useful in the estimation of the formation of these orbitals in the bonding between the atoms that make up a molecule.

The atomic orbitals combining to form molecular orbitals should have comparable energy. This means that the 2p orbital of an atom can combine with another 2p orbital of another atom, but 1s and 2p cannot combine together, as they have appreciable energy differences.

The combining atoms should have the same symmetry around the molecular axis for proper combination; otherwise, the electron density will be sparse. For e.g., all the sub-orbitals of 2p have the same energy, but still, the 2pz orbital of an atom can only combine with a 2pz orbital of another atom but cannot combine with 2px and 2py orbital, as they have a different axis of symmetry. In general, the z-axis is considered the molecular axis of symmetry.

The two atomic orbitals will combine to form a molecular orbital if the overlap is proper. The greater the extent of overlap of orbitals, the greater will be the nuclear density between the nuclei of the two atoms.

The condition can be understood by two simple requirements. For the formation of a proper molecular orbital, proper energy and orientation are required. For proper energy, the two atomic orbitals should have the same energy, and for the proper orientation, the atomic orbitals should have proper overlap and the same molecular axis of symmetry.

The space in a molecule in which the probability of finding an electron is maximum can be calculated using the molecular orbital function. Molecular orbitals are basically mathematical functions that describe the wave nature of electrons in a given molecule.

These orbitals can be constructed via the combination of hybridized orbitals or atomic orbitals from each atom belonging to the specific molecule. Molecular orbitals provide a great model via the molecular orbital theory to demonstrate the bonding of molecules.

The electron density is concentrated behind the nuclei of the two bonding atoms in anti-bonding molecular orbitals. This results in the nuclei of the two atoms being pulled away from each other. These kinds of orbitals weaken the bond between two atoms.

In the case of non-bonding molecular orbitals, due to a complete lack of symmetry in the compatibility of two bonding atomic orbitals, the molecular orbitals formed have no positive or negative interactions with each other. These types of orbitals do not affect the bond between the two atoms.

An atomic orbital is an electron wave; the waves of the two atomic orbitals may be in phase or out of phase. Suppose A and B represent the amplitude of the electron wave of the atomic orbitals of the two atoms A and B.

The energy levels of bonding molecular orbitals are always lower than those of anti-bonding molecular orbitals. This is because the electrons in the orbital are attracted by the nuclei in the case of bonding molecular orbitals, whereas the nuclei repel each other in the case of anti-bonding molecular orbitals.

The lowering of the energy of the bonding molecular orbital to the combining atomic orbital is called stabilization energy, and similarly, an increase in energy of the anti-bonding molecular orbitals is called destabilization energy.

Try this: Paramagnetic materials, those with unpaired electrons, are attracted by magnetic fields, whereas diamagnetic materials, those with no unpaired electrons, are weakly repelled by such fields. By constructing a molecular orbital picture for each of the following molecules, determine whether it is paramagnetic or diamagnetic.

The concepts of absolute electronegativity, chi, and absolute hardness, eta, are incorporated into molecular orbital theory. A graphic and concise definition of hardness is given as twice the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Useful correlations can now be made between chemical behavior, visible-UV absorption spectra, optical polarizability, ionization potentials, and electron affinities.

I am learning about MO theory in my advanced inorganic chemistry course and am starting to realize that it is truly the most accurate representation of how molecular orbitals look like, where they are located in the molecule, and their relative energies to each other and the original atomic orbitals from which they are composed of. We are using Symmetry Adapted Linear Combinations as the approximation method and so far this method has successfully explained all chemical/magnetic/electronic properties for any molecule investigated thus far.

In my opinion, inorganic chemists like MO theory so much because it's is the simplest theory of molecular bonding and geometrically its results are quite intuitive. It is an excellent conceptual tool for understanding quantum chemistry, but a horrible one for actual predictions of chemical properties.

Coupling between molecules and vacuum photon fields inside an optical cavity has proven to be an effective way to engineer molecular properties, in particular reactivity. To ease the rationalization of cavity induced effects we introduce an ab initio method leading to the first fully consistent molecular orbital theory for quantum electrodynamics environments. Our framework is non-perturbative and explains modifications of the electronic structure due to the interaction with the photon field. In this work, we show that the newly developed orbital theory can be used to predict cavity induced modifications of molecular reactivity and pinpoint classes of systems with significant cavity effects. We also investigate electronic cavity-induced modifications of reaction mechanisms in vibrational strong coupling regimes.

The use of strong light-matter coupling to modify molecular properties and reactivity is nowadays a very popular topic in physics and chemistry1,2,3,4. Many groundbreaking works have shown that interaction with confined fields can impact many matter features ranging from the modification of absorption and emission spectra5,6,7,8 to the alteration of photochemical processes9,10. In particular, the chemistry community has focused on how and to which extent reactions can be engineered by coupling with light11,12,13,14. Interaction with quantum fields can indeed significantly affect molecular processes both in the ground state and excited states15,16 with reported examples of reactions slowing down14, speeding-up17 or becoming selective towards one product18. The easiest way to achieve strong coupling between light and matter is through optical cavities (See Fig. 1a), where the frequency of the electromagnetic field is determined by the geometrical features of the device19. Inside the cavity, the photonic vacuum couples to the molecular system creating polaritonic states20 with distinct features21. Most importantly, the properties of the mixed matter-photon states can be engineered tuning the photonic part of the system, which means that polaritons represent a very effective way to modulate matter properties in a non-invasive way22.

a Pictorial representation of an optical cavity with an injection input, the coated glasses, and a spacer to regulate the distance between the mirrors. The frequency of the cavity fields is proportional to the inverse of the distance between the two mirrors. The lambda parameter quantifies the strength of the light-matter coupling. The cavity picture is based on a video realized by the Ebbesen group. b Origin invariance of the SC-QED-HF orbitals compared with the origin dependence of QED-HF orbitals. If the methoxy ion is displaced in space, both the orbital energies and the orbital shapes changes for QED-HF orbitals, while the SC-QED-HF orbitals remain unaltered. c Orbital modifications due to changes in the cavity parameters. Changing the cavity parameters (frequency and coupling) the electronic ground state and therefore the molecular orbitals are changed. Particularly, we show that an avoided crossing like situation can be observed among orbitals.

A detailed theoretical description of the strong coupling regime is urgently needed to develop an intuitive picture of cavity chemistry, that would also greatly ease the experimental design. However, this is a challenging task because in the strong coupling regime photons become a critical component of the quantum system and they must therefore be treated as quantum particles following quantum electrodynamics (QED). Only recently, a wider interest from the chemistry community in electron-photon systems has led to the introduction of semi empirical methods23, variational theories24 as well as many others25. Only four ab initio methods have been proposed so far: QED Hartree Fock (QED-HF)26, quantum electrodynamical density functional theory (QEDFT)27,28,29, QED coupled cluster (QED-CC)26,30,31,32 and QED full configuration interactions (QED-FCI)26,33. Molecular orbital theory for the strong coupling regime has so far not been proposed, although all the methods mentioned above use an orbital basis to parametrize the wave function26,34,35. The molecular orbital (MO) concept is a powerful theoretical tool used to develop correlated theories and to provide a qualitative and simple interpretation of molecular properties36. In particular, since MOs also display local properties of the system like the electrophilicity or nucleophylicity of atomic fragments, reactivity can in many cases be more easily rationalized in terms of orbitals, rather than with electron densities. The introduction of a MO theory for systems in QED environments may therefore significantly enhance our chemical intuition about experiments in strong coupling regimes. 2351a5e196