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Chemical bonding force

  1. Jul 21, 2011 #1
    Chemical bonding force. Help me understand how chemists describe this force!

    So one proton has a positive charge. One electron has a negative charge. When we bring them together, that makes one hydrogen atom. The positive proton and the negative electron cancel each other out. Perfect!

    But that single hydrogen atom is NOT happy on its own even though the proton and the electron cancel each other out.


    Why does that hydrogen want to stick to another hydrogen to form H2?

    Why would that hydrogen want to stick to a neutron to form Deuterium when a neutron is electrically neutral?

    What name do chemists use to describe the force that attracts 2 hydrogen atoms together?

    Any help would be appreciated. Sometimes its the simplest things that catch me out.

  2. jcsd
  3. Jul 21, 2011 #2
    Because H2 is lower in energy than 2 H atoms.

    You see, it's not quite a matter of positive and negative charges "cancelling each other out" - the charged particles still exist. But we know that it costs energy to separate a positive from a negative charge or, conversely, a positive and negative charge will be attracted to one another and be "happier" - i.e., lower in energy - if they're allowed to do so.

    Very broadly speaking, an H2 molecule is two protons sitting a little way apart with two electrons in between them. The real story is a little bit more complicated than that, not least because they have to be described using quantum theory, but that's the basic picture. Now each electron is close to both nuclei, and each nucleus is close to both electrons, so they are even "happier" than they were as individual atoms.

    (Of course, the nuclei are close now to each other as well, which makes them "unhappy" since positive charges repel one another, and a similar argument goes for the electrons. In some cases this positive energy contribution wins out - it's the reason why the He2 molecule doesn't exist, for instance. Working out precisely which of these interactions is most important, and whether a molecule is "happier" together or in pieces, is the topic of the entire field of quantum chemistry!)

    You're absolutely correct that the force holding neutrons and protons together in nuclei is not electrostatic in nature. There are four "fundamental forces" in the universe: gravity is one, electrostatic interactions are another. The other two are mysteriously called the "strong" and "weak nuclear forces", and it's the weak nuclear force that holds nuclei together. This is all a little complicated and is still the subject of a lot of research, but the main point to answer your question is simply that it's an entirely different set of rules that says nuclei should stick together - you can't understand it on the basis of the laws of electrostatics.

    The interatomic force, usually - but this is just a description rather than some brand new type of force.

  4. Jul 21, 2011 #3
    Every orbital around an atom is 'full' when two electrons of opposite spin occupy it, the spin could be viewed as a charge "canceling each other out" as well. Since a hydrogen atom only has enough charge to "happily" or neutrally have one s-orbital, to completely fill this orbital with electrons that cancel each other out, the atoms need to 'extend' their orbitals to encompass both atoms, this is what is called a covalent bond. This fills up their valence (outer) orbital, and everything is "Happy"! :D
  5. Jul 21, 2011 #4
    Modulated, That Neuron,
    Thanks for responding. Its doesn't seem to be clear cut at all. My problem is that i started learning about particle physics before i started chemistry. The particle physicists seem to have a completely different set of names for the forces and interactions. I can't seem to connect the particle physics with the chemistry. I'm sure some of the words they use are the same forces but chemists call these forces different names.

    What i do understand is that every molecule wants to be a noble gas, or at least have neutral properties of a noble gas. Noble gases are very happy, and it seems to me they rarely appear in chemical reactions cos nothing wants to stick to them, unless they get ionised or beta decay or something like that.

    And i can't get my head around this "8" thing. After helium, we have Ne, Ar, Kr, Xe, Rn and they all want to achieve this thing where they have 8 electrons in the outer shell. Is this a chemical geometry thing?. Kinda like the way the electrons start stacking in orbitals 3 dimensionally around the nucleus. Are the nucleons doing the same thing as the electron orbitals maybe? Maybe in the nucleus the nucleons are stacking themselves around each other similar to the orbital shells and and electron lobes.

    Ahhhhh.......maybe i just need to go away and read more until i get a handle on this. My problem is i came at chemistry from the wrong end. I started learning the very advanced stuff first hoping i could accelerate the learning process. But now i have snippets of very advanced stuff but i'm missing the basic chemistry.

    [EDIT] Let me add something here. I have a gut feeling its "spin" is whats causing the funny "8" stacking thing that goes on in the nucleus of the heavier elements. And i'm not talking about the spin of the electron. I mean the spin of the nucleons! Is that whats causing electrically neutral atoms to stick together? Spin is everything to the particle physicists! But i never hear the chemical guys talking about the "spin" of the nucleons.

    [EDIT 2] Yea, that must be it guys. If you look at the pattern the periodic table takes, each time we go down two levels in the table, the number of elements gets larger. The p block is only 6 elements wide, but the d block is 10 elements wide, and the f block is 15 elements wide. So as the elements get heavier, the nucleons must be stacking in a similar fashion to what we see with electron orbitals. But it must be the spin of the nucleons thats causing it maybe. Chemical guys are calling this force a different name than what the physicists use.

    [EDIT 3] Ok, is this it. The nucleus is forming a cube geometry. A cube has 8 corners, so after H and He, the nucleons must be stacking themselves in a cube geometry with the p block elements stacking to fill the 8 corners of the cube, kinda similar to the p and d electron orbitals. Then when we get to the d block elements, our cube is bigger but still has 8 corners and the 10 d block elements start filling themselves in around the cube geometry. By the time we get to the f block elements, our cube is starting to look more like a circle but the cube with 8 corners still dominates the geometry.
    This is all caused by spin, maybe. Maybe.....i don't know.

    Last edited: Jul 21, 2011
  6. Jul 22, 2011 #5
    Well, I think you'll find that reading up on electron particle physics will help you considerably. But other than supplying charge and allowing the various orbitals, all chemical reactions are electron based.

    Yes! this is true, Let me explain the octet (8) rule, it has to do with the x,y and z axis of the p electron orbitals. An s orbital has one spherical orbital, a Px orbital has a dumbbell shaped electron orbital thickest along the x axis away from the nucleus and thins as we travel closer to the nucleus, it then increases in thickness as we travel away from the nucleus, stopping entirely when it reaches the radius of the S orbital. Py orbitals have exactly the same property but along the y axis.

    Since there are three P orbitals (x,y and z) and one S orbital, and each orbital can hold 2 electrons, four orbitals * two electrons each = 8 electrons... our magic number. When all the potential electrons slots of an energy level (in this case n=2) have been filled by electrons of opposite spin there are no two electrons occupying the same four quantum numbers... so the pauli exclusion principle does not take effect.

    Other orbitals like d and f orbitals have more than one axis describing them... for example Dxy, Dxz, Dyz, Dx^2-y^2, Dz^2, this although it makes their shapes more complex, it also opens up more possibilities for orbitals... Increasing the amount of orbitals... i.e. 5 for D, and 7 for F.

    The reason a full valence shell is simply because of least 'exposed' energy, when an electron shell is complete it takes a lot of energy to pull it apart... because it fits together so well. Also a shielding effect makes a 3s electron vulnerable to being detached or reacted with... due to the blocked attraction of the nucleus.

    No, the cubic atom theory once had its hayday (good thinking though)... but why would an atom have cubic volume, when charge propagates through the inverse square law?

    It makes sense to have a semi-spherical atom doesn't it?
  7. Jul 22, 2011 #6
    That Neuron,
    Yea, you make better sense than me!! I think i understand that octet rule now. I was just thinking out loud so you guys would know where i'm going wrong.

    When i really start nit-picking in chemistry there are so many things to trip me up. Its like walking through a mine field.

  8. Jul 22, 2011 #7

    Don't worry about it, I do the same thing! lol, But when you nit pick, sometimes its best not to get hung up on a particular problem too much, and just move along (don't skim the book) to the next section, as after a while all the theories will start to fit together and make sense! :D, What chemistry class are you in? or just reading for fun?
  9. Jul 23, 2011 #8
    Ahhhhhh.....Its tricky, its not a class, its more a task i must complete in life. I have some complex problems to solve and the problems span several different area's of science. Chemistry is one of them.

    Thanks for your help Mr. Neuron, and thanks again to Mr. Modulated too.

  10. Jul 24, 2011 #9
    I may be mistaken but AFAIK, it is the strong force isn't it?
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