Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Formation of 2 pi bonds

  1. Dec 19, 2004 #1
    In ammonia, why the N atom is sp3 hybridized and not sp2 hybridized...since there are only 3 bondings...

    Also, in ethyne, that is H-C(triple bond)C-H.......for the formation of 2 pi bonds, why it is the unhybridized 2px orbital and 2py orbital of each C atom overlap with each other? How about the 2pz orbital?


    any help would be appreciated
     
    Last edited: Dec 19, 2004
  2. jcsd
  3. Dec 19, 2004 #2

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    In NH3, there are 4 electron pairs about the N atom - you're omitting the lone pair.

    The triple bond in [itex]H-C \equiv C-H [/itex] is basically a sigma bond using one of the two 2s electrons (the other 2s electron is used for the sigma bond with H), and a pair of pi bonds using both of the 2p electrons. Since C has only 2 electrons in the 2p subshell, and since px and py are lower energy orbitals than pz, the pi bonds must involve an overlap of only these orbitals.
     
  4. Dec 19, 2004 #3
    Gokul43201:

    but in my textbook, it is said that orbitals in the same subshell is at the same energy level...I am confused now....
     
  5. Dec 19, 2004 #4

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    For isolated Carbon atoms they do:[itex]2p_{x},2p_{y} & 2p_{z}[/itex] have all the same energy.But when the Carbon atom reacts with nonmetalic elements,like Hydrogen,those orbitals do not behave in the same manner.That's because 2 of them have one electron and the remaining one ([itex] 2p_{z} [/itex]) has none.The 2 orbitals with one electron they "hybridize" with the [itex] 2s [/itex] orbital which has 2 electrons,resulting in 4 hybridized orbitals of smaller energy than the unhybridized [itex] 2p_{z} [/itex].Since it overlaps 3 hybrid orbitals (one [itex]\sigma [/itex] and 2 [itex] \pi [/itex]) with another C atom,it has a triple bond.Since 2 of the bonds are [itex]\pi [/itex],and another 2 are [itex] \sigma [/itex],it id hybridized [itex] sp [/itex].


    Daniel.

    PS.Maybe Gokul can put it in a more coherent way... :wink:
     
  6. Dec 19, 2004 #5

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As Dexter mentioned, your textbook is right only when it talks about isolated atoms.

    However, when a molecule is being formed, the direction along the line joining the atoms breaks the degeneracy (x, y and z are not symmetric anymore; the z direction is the internuclear direction and so, is different from x and y) between px, py and pz.
     
  7. Dec 19, 2004 #6

    GCT

    User Avatar
    Science Advisor
    Homework Helper

    A "pz" pi molecular orbital would be along the same axis as the sigma, perhaps this clarifies things a bit more.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Formation of 2 pi bonds
  1. Sigma and Pi bonds (Replies: 9)

Loading...