What is Molecular orbitals: Definition and 24 Discussions

In chemistry, a molecular orbital is a mathematical function describing the location and wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The terms atomic orbital and molecular orbital were introduced by Robert S. Mulliken in 1932 to mean one-electron orbital wave functions. At an elementary level, they are used to describe the region of space in which a function has a significant amplitude.
In an isolated atom, the orbital electrons' location is determined by functions called atomic orbitals. When multiple atoms combine chemically into a molecule, the electrons' locations are determined by the molecule as a whole, so the atomic orbitals combine to form molecular orbitals. The electrons from the constituent atoms occupy the molecular orbitals. Mathematically, molecular orbitals are an approximate solution to the Schrödinger equation for the electrons in the field of the molecule's atomic nuclei. They are usually constructed by combining atomic orbitals or hybrid orbitals from each atom of the molecule, or other molecular orbitals from groups of atoms. They can be quantitatively calculated using the Hartree–Fock or self-consistent field (SCF) methods.
Molecular orbitals are of three types: bonding orbitals which have an energy lower than the energy of the atomic orbitals which formed them, and thus promote the chemical bonds which hold the molecule together; antibonding orbitals which have an energy higher than the energy of their constituent atomic orbitals, and so oppose the bonding of the molecule, and nonbonding orbitals which have the same energy as their constituent atomic orbitals and thus have no effect on the bonding of the molecule.

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  1. M

    Identification of HOMO/LUMO in radicals

    Hello, as the title says, how do you treat singly occupied orbitals in radical molecules, when trying to identify the HOMO and LUMOs? In the majority of cases I stumbled upon, like O2, both the antibonding orbitals, pi*2px pi*2py, are singly occupied, so they would be considered the HOMO, with...
  2. LUFER

    Wavefunction Equations Of Hybridized Orbitals

    Hi, I'm looking for the equations to perform the wave function of the orbitals, that way I can give a graph. The problem I only encounter situations in basic energy transfer (valence).Task: Make wavefunctions of the sp2, sp3, sd3 hybridized orbitals respectively. I need the wavefunction...
  3. Dario56

    I Why Does Molecular Potential Energy Curve Have That Specific Shape?

    Molecular potential energy of hydrogen in dependence with atomic distance for bonding orbital is given by picture below. We can see that at large distances force between atoms is attractive and potential energy drops to minimum which corresponds to bond energy and length. This part of the...
  4. N

    A Typical binding energies of sigma-orbitals

    I'm interested in typical electron binding energies of conjugated materials such as pentacene. The carbon 1s energy is easy to find in literature (-285 eV), typical 2π and 2π* binding energies are in the range of few eV (-10 eV ... -2 eV) depending on the size of the conjugated system. But...
  5. Helena Wells

    Energy differences of molecular orbitals

    Suppose we have a molecule A-A and a molecule A-B . And we want to compare the differences in energy of the different molecular orbitals for example the 1s antibonding orbital with the 2s bonding orbital.How can we do that?
  6. sams

    Calculating the Molecular Orbitals of a Molecular State

    I am performing ab initio calculations on a heteronuclear diatomic compound using the MRCI method on the MOLPRO quantum chemistry package. I obtained the molecular states of the compound but I was wondering how to find the molecular orbital configuration of each electronic state in addition to...
  7. Sophrosyne

    B How to think of molecular orbitals quantum mechanically

    The electrons in a molecule are said to be in a quantum superposition state in terms of their position/spin/momentum. But when you look at a molecule like water at a chemical level, it has a very specific shape corresponding to the P orbitals of the outer shell of the Oxygen atom. The two...
  8. C

    How to Keep Up with Molecular Orbitals for Intro Chemistry

    I am a professional math and science tutor, primarily focused on math and physics. I used to tutor organic chemistry but gave it up because I didn't want to study orgo an hour per week for the rest of my life. I like general chemistry and have no trouble with most topics, but the way of...
  9. W

    How Do Orbital Interactions and Sigma Bonds Work in Methane?

    Hello all I have an exam coming up this week but there's something that I don't understand: Let's take methane, for example. If I understand it correctly, the bonding orbitals of carbon are all hybridized to sp³ orbitals and overlap with the 1s orbital of four H atoms. Does the orbital of...
  10. H

    Chemistry Bonding and antibonding molecular orbitals

    Not a homework question, just curious. My book says that bonding orbitals from from constructive interference while antibonding orbitals from destructive interference. Since constructive interference increases amplitude, what increases in amplitude from the combination of bonding orbitals? It...
  11. N

    Molecular Orbitals: Understanding & Rules

    My general understanding of Molecular Orbitals is as follows: N atoms come together to form N molecular orbitals. N/2 of the orbitals will be spatially asymmetric with symmetric spins.This corresponds to the antibonding orbital. N/2 will be spatially symmetric with antisymmetric spins. This...
  12. H

    Molecular orbitals of three or more atoms

    In Molecular orbital theory, when two atoms A & B come close to each other, their atomic orbitals (say their s orbitals) combine and make two molecular orbitals, one bonding and the other anti-bonding. How about molecular orbitals of three or more atoms? For three atoms say A & B & C we would...
  13. P

    Molecular orbitals sigma and pi

    hi! i have a doubt, how can i know the total number of bonding and antibonding electrons given a diatomic molecule's electronic configuration in therms of sigma and pi orbitals? I have to add these σ and π orbitals are of the type gerade and ungerade. does anyone can help me?
  14. M

    Molecular Orbital Theory: Build MOs for Diatomic Molecules

    http://chemwiki.ucdavis.edu/Theoretical_Chemistry/Chemical_Bonding/Molecular_Orbital_Theory/How_to_Build_Molecular_Orbitals Hi, I'm currently trying to understand MO theory and how diagrams are made and interpreted. I stumbled across this website and it shows the general MO diagrams...
  15. A

    Energy Bands and Molecular Orbitals

    Hello, a newbie here. I need to understand the relationship between MO and Energy Bands. Although i have searched and researched about this topic in Google, but i am yet to understand this part clearly. It is said that Energy Bands occur as the number of MO increase due to the various...
  16. B

    Localization of Molecular Orbitals

    Just curious why chemical physicists bother with localization procedures for molecules. Because atomic orbitals become de-localized when they form molecular bonds, but then it seems people wish to come up with procedures to re-localize. I've read quite a bit on how the de-localization...
  17. T

    Anti-Bonding/Bonding Molecular Orbitals

    Can someone explain to me, what are the factors/reasons that when certain atoms bond together, they form anti-Bonding or Bonding Molecular Orbitals? I am confused, and this is not in my syllabus(equivalent to Grade 12). P.S. It would be helpful if you included wavefunctions as well.
  18. S

    Molecular orbitals don't get it

    Molecular orbitals... don't get it Hi I'm new, to this forum and molecular science Reading a bit about molecular orbitals, and I have to say the whole concept of anti bonding orbitals and bonding orbitals got me quite confused. when atomic wave functions add you get bonding orbitals when...
  19. M

    Molecular Orbital Theory: 2s/3s & 2p Orthogonality Questions

    I have a few questions on molecular orbital theory which I hope you guys can help me settle! So I understand orthogonality meaning that the molecular orbitals have zero overlap, due to the Pauli Exclusion Principle. How do a 2s and 3s molecular orbital achieve orthogonality? Is it due to a...
  20. G

    Exploring Wave Functions & Molecular Orbitals: Questions & Answers

    I have one question about wave functions and molecular orbitals (MO). In the computational quantum chemistry scientists often use Linear Combination Atomic Orbitals (LCAO) to construct MO. \varphi_{i\lambda\alpha}(\vec{r})= \sum\limits_{p=1}^{N}\chi_{p\lambda\alpha}(\vec{r}) C_{i\lambda p}...
  21. L

    Individual contributions of molecular orbitals to the total density of states

    Hi, I have a question regarding the contribution of some molecular orbitals (e.g HOMO, LUMO) to the total density of states of a two-probe system. How exactly are the contributions of the MO ( that look similar to the DOS plots ) calculated, do they have something to do with the local...
  22. A

    Atomic Orbitals vs. Molecular Orbitals and Hybridization

    Hey everyone! I was wondering, when orbitals are hybridized, new hybrid Atomic Orbitals (AO) are formed. Now, when these hybrid atomic orbotals bond with another atomic orbitals, are molecular orbitals formed? For example, when 2 Hydrogens bond to form H2, the 1s orbitals overlap to form 2...
  23. N

    What are the shapes of molecular orbitals?

    Please, can someone answer my question? I know the shape of sp hybrid orbital, but want to know about the others ( sp2,sp3,dsp2,dsp3,d2sp3,d3sp3 ). And are there any other type of molecular orbitals?
  24. M

    Molecular Orbitals: Carbon Nanotubes, Silicon & More

    While learning about carbon nanotubes I ran into the term molecular orbitals. I know something about atomic orbitals but took chemistry a long time ago. I would expect the concept of molecular orbitals to be useful for covalent bonding like Silicon crystals and metals. I would expect it's...