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What does it mean by an overlap of orbitals? Watch

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    I've started to do some revision on Carbonyl compound (Aldehydes and Ketones) and I don't understand what it means by:

    *Sigma bond formed by "overlap of orbitals" between Carbon and Oxygen atoms.
    *Pi Bond is formed by the "overlap of of p orbitals" on the Carbon and Oxygen atoms.
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    It means quite literally that the orbitals overlap - A sigma bond is just a 'single bond'. The orbitals overlap because the two atoms 'share electrons'.

    In the case of a pi bond, this is just a 'double bond' - eg C=O or C=C.
    A p orbital on each atom (which looks like the figure 8 above and below the plane) overlaps to form an electron density above and below the sigma bond.

    hope this helps,
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    (Original post by mulac1)
    It means quite literally that the orbitals overlap - A sigma bond is just a 'single bond'. The orbitals overlap because the two atoms 'share electrons'.

    In the case of a pi bond, this is just a 'double bond' - eg C=O or C=C.
    A p orbital on each atom (which looks like the figure 8 above and below the plane) overlaps to form an electron density above and below the sigma bond.

    hope this helps,
    Careful here...

    a pi bond is not a double bond.

    A double bond is made up of one sigma (direct orbital overlap) bond and one pi (lateral orbital overlap) bond.
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    yeh thats true a double bond is a sigma and a pi bond together
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    It's the distinction between molecular orbitals, and atomic orbitals. Atomic orbitals you know are S, P, D, F etc. Molecular orbitals can sort of be thought of as their counterparts in molecules. S -> sigma, P -> pi, D-> delta etc.

    Now. Let's ask the question: What defines each atomic orbital? What defines each atomic orbital is the number of so called 'nodal planes' within it. An s orbital for example is a sphere and the electron density in this sphere is all of the same phase (imagine the electron as being a wave all in the same phase - assuming you've done physics). A p orbital has 1 nodal plane. It consists of two lobes (areas of high electron density) one of these lobes is in one phase and the other is in a comparative anti-phase so between these two orbitals you have an area (plane) where there is precisely 0 probability of an electron existing this is due to the so called wavefunctions (again just imagine an electron as being a wave, and think of what happens if you add two waves of opposite phase together) of these electrons cancelling out. And likewise with d orbitals you have 2 nodal planes.

    Molecular orbitals are also defined this way. A sigma orbital happens when to s orbitals form a bond, and it has no nodal planes within this 'molecular orbital', (a sigma bond can also occur when two p orbitals combine head on, or two d orbitals combine head on). A Pi bond consists of an orbital with one nodal plane. So you can sort of imagine this as being like having 2 sigma bonds running paralell to one another with a nodal plane inbetween.

    I'm hoping that I've given you a fairly full and satisfactory answer about what sigma and pi bonding is, and haven't just ended up confusing you further.

    My advice though would actually be to look at diagrams of atomic and molecular orbitals online, and see for yourself what I'm saying. It's a lot clearer if you can visualise it, and there are plenty of diagrams out there.

    Also don't think too hard about what I've said if you don't want to. What I've gone over is undergraduate level, not a level, but I thought it would be beneficial to try and give you a fuller picture, and a more rigorous definition of what the different molecular orbitals are.
 
 
 
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