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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37 views

When we write nd* in electron configurations, does that have anything to do with antibonding orbitals? (n = electron layer) [closed]

The title says it all. For example, when we make a sigma* or pi* antibonding orbital, does that correlate to excited electrons, especially in transition metals? Or is that a different topic? Thanks
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Can s-p mixing occur in all second period diatomic molecules?

Due to the s-p mixing in $\ce{Li2}$ to $\ce{N2}$ homonuclear diatomic molecules, 2p sigma molecular orbitals have higher energy than 2p pi molecular orbitals. My question is: which statement is ...
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Why don't molecules like water and hydrogen sulfide feature their two hydrogen atoms on exact opposite sides of the center?

I just saw a diagram of hydrogen sulfide, and it's two hydrogen form an angle of 92.1° with each other and the central sulfur atom.... With water its 104.45°... Why don't two identical atoms like two ...
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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 does hyperconjugation changes bond order in alkenes?

I am a high school student and I am little bit confused in hyperconjugation of alkenes, 1)In my textbook its written that bond order of C=C bond changes due to hyperconjugation {sigma-pi resonance) ...
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1answer
100 views

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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47 views

Does negative and positive signed s atomic orbitals exist?

In the sense of one atom, I have read that the sign of the orbitals has little meaning. I'm skeptical of this because the way atoms behave in bonding must be determined by the properties of the atoms ...
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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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How is it possible for a nucleus of an neutral atom to attract the electron cloud of another neutral Atom? [duplicate]

Because actually both have no external electric field when they are neutral.
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123 views

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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58 views

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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2answers
63 views

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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37 views

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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1answer
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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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1answer
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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 ...
5
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1answer
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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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1answer
136 views

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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1answer
58 views

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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1answer
51 views

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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35 views

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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53 views

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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1answer
101 views

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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1answer
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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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1answer
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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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2answers
56 views

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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51 views

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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54 views

How to use MO theory for compounds containing 3 atoms?

We have been taught MO theory, and I have learned how to use it for compounds containing 2 atoms. Can we use this theory for compounds like sulphur dioxide, with more than three atoms? If possible, ...
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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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68 views

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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103 views

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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1answer
65 views

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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2answers
310 views

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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1answer
62 views

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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1answer
241 views

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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1answer
72 views

Why d and s orbitals overlap even when there is considerable difference in their energies?

In my grade 11 chemistry NCERT textbook, its written that hybridization happens when orbitals of almost same energy overlaps. But S orbital and D orbital have significant difference in their energies. ...
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First ionization energy and electron gain enthalpy of dihydrogen / stability comparison of dihydrogen ions [duplicate]

Subset of: How can antibonding orbitals be more antibonding than bonding orbitals are bonding? Stability of $\ce{H2^{-}}<\ce{H2^{+}}<\ce{H2}$ Stability of $\ce{N2^{-}}<\ce{N2^{+}}<\ce{N2}...
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How can orbitals of Hydrogen and Chlorine atom combine to form molecular orbitals of Hydrogen Chloride? [closed]

Linear combination of atomic orbitals (LCAO) states that orbitals can only combine if the energies and shape of the orbitals are same. $3p$ orbital of Chlorine and $1s$ orbital of Hydrogen are the ...
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47 views

Spin Multiplicities of Ions

The multiplicity is fundamentally defined as $2S + 1$ where $S$ is the total spin. From what I understand, the multiplicity corresponds with the number of unpaired/paired electrons. For example, in ...
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molecular orbital theory and crystal field theory confusions

I am a high school student and I am very confused in Molecular orbital theory, it says that when two orbitals overlaps in the same phase, they form antibonding orbitals and when they overlap in ...
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143 views

Explanation of the trans-effect (thermodynamic and kinetic) for octahedral transition metal complexes

The thermodynamic trans effect refers to the ground state weakening of the metal-ligand bond in a complex by a ligand trans to it. The kinetic trans effect is the lablisation of a ligand in a complex ...

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