Questions tagged [molecular-orbital-theory]

Use of molecular orbital (MO) theory allows for an understanding of the observed properties (shape, reactivity) of molecules. 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.

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Do diatomic isoelectronic molecules have the same bond order even when the octet rule is not followed?

It can be observed and proven that diatomic isoelectronic molecules have the same bond order when they follow the octet rule (upto 3rd period elements). But what about when they do not follow the ...
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What is the energy ordering of molecular orbitals in diatomic molecules of third and fourth period elements?

For diatomic molecules with less than 16 electrons, the list of molecular orbitals in order of increasing energy is: σ1s < σ*1s < σ2s < σ*2s < (π2py = π2pz) < σ2px < (π*2py = π*2pz) &...
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Orbitals in benzene and other delocalised structures

I've read that molecular orbital theory demands that if there are $n$ orbitals prior to some event like bond formation, there should be $n$ orbitals after this event. Does this hold even in structures ...
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How do the spin-matrices change in systems without spherical symmetry?

The (non-relativistic) spin matrices of a free electron, with $z$ as the quantization axis, read: $$ \boldsymbol{S}_{x}=\frac{\hbar}{2}\left[\begin{array}{ll} 0 & 1 \\ 1 & 0 \end{array}\right],...
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What theory accurately explains metallic bonding in beryllium?

Since beryllium is an alkaline earth metal, the bonds between beryllium atoms could be considered metallic and we can use molecular orbital theory (MOT) to explain metallic bonds in metals. Consider ...
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pKa of methylene protons in cycloheptatriene vs cyclopropene

The $\mathrm{p}K_\mathrm{a}$ values of methylene protons in cycloheptatriene vs cyclopropene are found to be 60 and 36, respectively. From what I understand - both conjugate bases are non-aromatic (...
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Why is this diagram depicting the molecular orbital (MO) basis for a back-side attack the way it is?

Consider: The description of this image in my textbook is as follows: In order to form a bond, the HOMO (the highest occupied molecular orbital) of one species must interact with the LUMO (the ...
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Explanation of the missing 1-s orbital electrons of carbon in the molecular orbital diagram of methane

Consider the molecular orbital diagram of methane, for example found here: I would like to know what happens with the two 1s orbital electrons of carbon in the molecular orbitals it is forming. Is it ...
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Crystal Field Splitting Energy - Tetrachlorocuprate and Tetrachlorocobaltate

I'm a high schooler from India and it's my first time on this stack exchange. I was wondering why the crystal field splitting energy of tetrachlorocuprate differs so much from tetrachlorocobaltate. ...
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Why are the 1s bonding and antibonding molecular orbitals excluded while making Molecular Orbital diagram for diatomic homo/heteroatomic molecules?

Do these molecular orbitals not form or are they left out as something general that doesn't require repeated mentioning? I'm in my first semester of college so please keep the explanation simple:)
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Why is octaoxygen diamagnetic?

I tried considering that according to LCAO-MO theory $\ce{O2}$ is paramagnetic, which is confirmed by experimental evidence. Since octaoxygen has the crystal structure in figure, I thought there is a ...
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Molecular orbital theory and Lewis structure for dioxygen

I am a bit confused about how molecular bond theory predicts pairings of unbounded electrons. For example, in $\ce{O2}$ there are two pairs of electrons on each oxygen along with the double bond. ...
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How does the MO-LCAO theory explain the direction of valence bonds?

As all the bells sound, the common explanation of geometry of a molecule (consider the water molecule) is due to overlaping electron density. The valence bond theory of the water molecule describes ...
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How do you draw the pi MO diagram for the acetate ion CH3COO-

How do you draw the pi MO diagram for the acetate ion CH3COO- ? I get stuck with the number of electrons on the 2p orbital of Oxygen atom. My teacher said 1 oxygen has 1e, the other has 2e. But ...
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How can I use the MO diagram of hydrogen fluoride to demonstrate that the molecule is polar?

I am trying to explain that HF is a polar molecule using the MO diagram. Normally I say that the F atom has a higher electronegativity than the H atom, which causes a net positive dipole moment. ...
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When pigments absorb light only around a single particular wavelength, why aren't they still white?

I'm trying to understand how organic molecules get their colour. One major factor are conjugated double bonds which create delocalized pi-orbitals (e.g. https://en.wikipedia.org/wiki/...
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Can two noble gases attract each other?

If two hydrogen atoms are far apart, they have no effect on one another. But as they are bought closer together, they begin to excerpt an effect. The two nuclei, having the same positive charge, repel ...
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What is the LUMO and HOMO in and O2 diatomic

In the molecular orbital (MO) diagram for the $O_2$ diatomic, the $2π_g^*$ contains two unpaired electrons. This is certainly the HOMO, as it is the highest molecular orbital with electrons. My ...
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Why are anti bonding orbitals distorted towards the less electronegative element?

Bonding molecular orbitals are distorted towards the more electronegative atom and so the atomic orbitals from this atom contribute more to those bonding orbitals. This implies that anti bonding ...
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Electronegativity, polarity, pi bonds, and nitriles

While googling some numbers, I found that the dipole moment of acetonitrile is, according to wikipedia 3.92D. Compare this to the dipole moment of ethylamine, according to NIST of 1.220D. Now, I've ...
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Determination of energies in MO diagrams

How do we determine the relative placements of molecular orbitals in their diagrams? I understand that we can use point groups to find symmetry-allowed interactions between orbitals that we write on ...
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Contribution, and the way thereof, of the core 6p orbitals of compounds of plutonium(VIII)

According to the NIST database, the ground-state configuration of plutonium(VIII) is [Hg]5f³6p³, when intuitively it should be the same as neutral radon([Hg]6p⁶). Since plutonium(VIII) compounds are ...
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What does it mean for an electron to be in a bonding/antibonding orbital?

My confusion arises from the fact that bonding and antibonding orbitals are created simultaneously. I have read this answer that clarifies about the existence of the molecular orbitals itself. But now ...
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How are the energies of natural atomic orbitals calculated when they are, strictly speaking, not "meaningful" wavefunctions?

There are several programs that can calculate the "energies" of the natural atomic orbitals(NAO) that come from NBO analysis. However, I have several evidence that, unlike the energies of ...
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Why SCF procedure in Hartree-Fock doesn't keep returning the same coefficients?

In the context of Hartree-Fock theory, using Roothaan formalism, we write: FC=SCE where F is the matrix of the Fock operator, C are the coefficients to be used in the construction of the wave function ...
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Justification for using valence bond theory and molecular orbital theory together?

Elementary gen chem books will make the careful distinction between the two theories and then proceed to claim that chemists can use both to complement each other to explain the behavior of certain ...
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How can Phthalocyanine be aromatic when it is not planar? [closed]

Even as Hückel's rule is not applicable in every scenario, especially in metallic clusters, it seems that organic structure need to be planar to show aromaticity. That being the case, Pubchem's ...
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1 answer
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Which ion has a greater paramagnetic property?

I just recently began studying the Molecular Orbital Theory in Chemistry and I just learnt about the paramagnetic and diamagnetic nature of molecules based on their unfilled and filled orbitals. Now ...
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Why are HOMO and LUMO energies invariant under spin-flip?

Atomic theory says singlet and triplet energies for the same orbital differ because of exchange interaction. However, molecular orbital (MO) theory describes the energy between the HOMO (highest ...
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Does the 1s orbital have two different phases? [duplicate]

How can the 1s orbital (in H atom for example) interfere both constructively and destructively (to give rise to bonding and antibonding molecular orbitals) with another 1s orbital, if the 1s orbital ...
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For benzene, why are the first three pi molecular orbitals considered bonding, and the higher three antibonding?

Is it because all the molecular orbitals that are naturally occupied are all considered to be bonding orbitals? So for benzene, since the lowest three orbitals are all occupied (due to benzene having ...
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Why does the same type of hybridization appear in both Valence Bond Theory and Molecular Orbital Theory?

I was reading about Molecular Orbital Theory, and saw that you can treat a central atom's atomic orbitals as hybrid orbitals in order to simplify the process of creating molecular orbitals by no ...
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Why exactly is the conduction band in semiconductors conducting?

Is it because when the electrons are excited to a higher energy level, they can lose energy and fall back down to lower energy levels? Due to the sheer number of antibonding MOs in the conduction band,...
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Does overlapping partial density of states indicate formation of chemical bond?

Does overlapping partial density of states of two adjacent atoms indicate formation of chemical bonds between the two atoms? The partial density of states here means the density of states of an ...
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What is the exact Hamiltonian core of the Fragment Molecular Orbital Method?

My major is not chemistry and I am trying to understand the Hamiltonian core of the Fragment Molecular Orbital (FMO) method. I think it should be the normal Hamiltonian core of the restricted Hartree-...
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In the LCAO method for $H_2^+$, why do we only add or subtract orbitals but never alter one of the phases of the orbitals?

TLDR: Atkins' physical chemistry contains the quote "In general, from N atomic orbitals we can build N molecular orbitals". In the case of $H^+_2$, we use a combination of N=2 orbitals to ...
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Molecular orbitals in an ionic diatomic compound

The wavefunction of a heteronuclear diatomic molecule, after the orbital approximation and the Born-Oppenheimer approximation, is $$\psi = c_A \chi_A \pm c_B \chi_B $$ where $\chi$ are the starting AO ...
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Relation of partial charge with wavefunction

Suppose we have an one electron system. The probability $P$ that electron's position is in some interval $x + dx$ is given by: $$P = \int_x^{x+dx}|Ψ(x)|^2 dx$$ So if we measure $N$ times the electron'...
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Why is the sum of the square of the orbital coefficients 1

I'm reading up on molecular orbital theory and LCAO in Ian Fleming's "Molecular Orbitals and Organic Chemical Reactions" and I don't understand the logic here: "When there are electrons ...
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Do different types of MOs have different occupancies?

There was a question in my textbook regarding the number of electrons in a molecular orbital. The maximum number of electrons in a sigma, pi, and delta molecular orbital are respectively? Now, I ...
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$\pi$ Molecular orbital diagram of compounds like urea, guanidine, acetone etc

In my organic chemistry course, we've only been taught about how the $\pi$ MO diagrams of compounds like butan-1,3 diene, hexan-1,3,5 triene and similar single chain compounds look like. I was ...
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C=C and C=O bonds in molecular orbitals

For both $\sigma$ and $\pi$ bonds: A. In terms of electronegativity: Since effective nuclear charge of $\ce{O}$ is higher than $\ce{C}$, so the E.N. of $\ce{O}$ is higher than $\ce{C}$. Therefore, ...
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Does (BeCl2)n have 3c - 4e- bonding or not?

The title really explains what the issue is here. I would think that it has multicenter bonding akin to $(\ce{BeH2})_n$ polymer because they are pretty much iso-structural (although it shouldn't have $...
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How can 2 molecular orbitals form simultaneously? [duplicate]

I understand (for example in the case of H2) that two s orbitals produce through constructive interference a bonding orbital and that the out of phase combination of two s orbitals leads to ...
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Is strength of pi bonds greater than sigma bond of nitrogen molecule?

I am referring to molecular orbital (MO) theory. In the nitrogen molecule (and elements of lower atomic number) $\textrm{sp}$ mixing occurs and the sigma orbital set is raised above the pi orbital set....
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Computational determination of the diagram of molecular orbitals of a polyatomic chemical species

A diagram of molecular orbitals for $\ce{H2O}$ would be as follows: The above diagram has been constructed qualitatively following the steps that I have been instructed in various classes on this ...
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Question regarding conflicting results of checking the electron-preciseness of isoelectronic species via NBO and EHM calculations

It is well known that the tert-butyl cation's empty 2p orbital on the central carbon is stabilised by hyperconjugation from neighboring C-H bonds. This would mean that the central 2p "lone pair&...
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6 votes
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What is the correct molecular orbital diagram for the d orbitals in platinum for the tetraammineplatinum(II) complex?

I am trying to construct the diagram of $\mathrm{d}$ orbitals in the tetraammineplatinum(II) complex. According to the angular overlap model, $\mathrm{d}$ orbitals are going to look like those in the ...
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Molecular orbitals energy under pressure

Suppose we have a hydrogen molecule $\ce{H2}.$ At room temperature the average distance of the nuclei is $r_0$ (without applying pressure). If we put $n$ hydrogen molecules in a box with volume $V_\...
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Construction of the molecular orbital diagram for a species M4

I need to construct the molecular orbital diagram for the hypothetical species ${Li_4}$, which has the following geometrical arrangement: The first step is to identify the point symmetry group. In ...
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