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

Questions about covalent bond

  1. Feb 12, 2016 #1
    I have few questions trying to understand covalent bond in the simplest molecule H2 of two Hydrogen atoms.

    1. Can covalent bond be created between two hydrogen atoms for which electrons have parallel spin? That is, electron in first hydrogen atom has spin UP and electron in the second hydrogen atom has also spin UP.

    2. What determines whether covalent bond will be created with bonding or antibonding state?

    3. Since antibonding state has higher potential energy than the two individual neutral hydrogen atoms, then how it can ever be created?

    4. This final question is about covalent bond in multielectron atoms... Say we have nitrogen molecule N2 which has 3 covalent bonds. I understand that 3 pairs of electrons in the outer (valence) shell form three covalent bonds but are inner shell involved in covalent bonding as well? That is, 1s and 2s orbitals (nitrogen electron configuration is: 1s2 2s2 2p3).
    I am confused about this because at first I thought that only valence electrons form covalent bonds but in my book there is a graph for this molecule that shows that beside valence bonds there are also two sigma states (one bonding marked as σ1s and one antibonding marked as σ*1s).
     
  2. jcsd
  3. Feb 12, 2016 #2

    DrDu

    User Avatar
    Science Advisor

    There is no such thing as an anti bonding state
     
  4. Feb 12, 2016 #3
  5. Feb 12, 2016 #4

    DrDu

    User Avatar
    Science Advisor

    What I am saying is that you have to distinguish between antibonding orbitals (which are a theoretical construct) and whether the molecules can be in an antibonding state (which is not the case).
     
  6. Feb 12, 2016 #5
    Ok I acknowledge that. Do you know answers to my questions?
     
  7. Feb 12, 2016 #6

    DrDu

    User Avatar
    Science Advisor

    I think I already answered your questions 2 and 3. Sorry if my answer was a little bit condensed, but I answered from my phone.

    Concerning 1, two hydrogens with anti-parallel spin will always repell each other. Hence there is no covalent bonding.

    Question 4 is the most difficult to answer. The two 1s states will repell each other, but, as they are more compact than the valence orbitals, this repulsion can be overcome by the bonding interaction of the valence electrons. The repulsion of the 1s functions is due to the fact that the antibonding orbitals are so to say more antibonding than the bonding orbitals are bonding, so that a net repulsion remains even if both are filled.
    There is also another point: If both the bonding and anti-bonding orbitals formed from a set of atomic orbitals (e.g. the 1s orbitals) are completely filled, then the molecular wavefunction can also alternatively be described as being made up of the atomic orbitals without combining them first into molecular orbitals. Hence it looks like the electrons in the 1s orbitals are little influenced by the bonding of the valence electrons.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Questions about covalent bond
Loading...