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Thread: Where does the energy come from in formation of ions?

  1. #1 Where does the energy come from in formation of ions? 
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    Atoms tend to gain or lose electrons to have their orbitals stable. My question is if an atom has only so many protons, how could it gain more electrons. If the total positive charge is only 9 protons, for example, how could that atom have 10 electrons? What energy holds that extra electron in place?
    Also, why are atoms more "stable" when they complete their orbitals in a certain energy level?


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  3. #2  
    Forum Junior c186282's Avatar
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    You should not think of the electrons as balls zooming around the nucleus. But think of oddly shaped probability distributions that describe where the election could be found if you were looking (looking => making a measurement ). If the inner electrons clouds have a cumulative "odd" shape then the positive charge of the nucleus is not completely masked.
    This makes it possible for another electron to be captured.

    This has been a very hand waving argument and should be taken with a grain of salt.


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  4. #3  
    Forum Masters Degree organic god's Avatar
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    the answer to the question really depends on what level of chemistry you are at

    the question of stability on completing an energy level i think is best answered using MO theory.

    if you look at some simple diatomic molecules like nitrogen. you will see that this exists N2. this is because the two atoms ( N--N)
    will form a total of 6 molecular orbitals. 3 bonding and 3 anti bonding.

    the bonding effect of the s orbitals will cancel out with the anti bonding s orbitals. so do not contribute to the bond order

    however the remaining electrons will go into bonding orbitals formed from overlap of p orbitals. whilst the antibonding orbitals are empty.

    The bonding orbitals formed are of a lower energy than the p orbitals of the individual atoms this means that the atom will be in a lower energy state hence more stable
    everything is mathematical.
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  5. #4  
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    As for the first post, even if electron's are considered as probability waves and statistical distribution regions, they still have charges. If they do not fully cover the positive charge of the nucleus, then that means there is not enough positive charge to hold the electrons that are already present in their orbitals.

    In reference to the second post, I'm not exactly sure what antibonds are since I'm only in grade 11 chemistry, but I think I got an idea of what you are explaining. Thanks!
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  6. #5  
    Forum Masters Degree organic god's Avatar
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    basically when two orbitals overlap, 2 orbitals must be created. one of these is a bonding orbital the other is an antibonding orbital. the antibonding orbital is higher in energy than the isolated atom
    everything is mathematical.
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  7. #6  
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    Cut-and-pasted from another thread:

    It mostly has to do with how much positive charge from the nucleus the electrons in the outer shell experience (which is usually called Z-effective or Zeff), which depends on the principle quantum numbers of the electrons involved.

    The octet rule occurs mainly because an electron around a nucleus will not perfectly "shield" another electron from the nucleus's positive charge, especially if the shielding electron and the incoming electron have the same principle quantum number. 2p electrons can't shield other 2p electrons very well (and 3p can't shield other 3p very well, etc.). It's kind of complicated, but I will explain it as best I can.

    Consider a helium atom and a hyrogen atom (a proton). If I only give my He atom one electron and give my proton no electrons, both my He and my proton will have a charge of +1. Since they have the same charge, you might think that an electron would be equally attracted to either one - but that's not the case. An electron is much more strongly attracted to an He+ atom than to a H+ atom. This occurs because even though the He+ and the H+ have the same charge, the He has two protons and the electron that's already present won't perfectly shield the incoming electron from one whole unit of positive charge. The result is that an electron coming into an He+ atom will experience a positive charge that's something like +1.3 insted of just +1. How well an electron shields an outer electron from the nucleus depends on the principle qunatum number and angular momentum quantum number of the electrons involved. If an electron has the same n and l value as the electron that it's trying to shield, it won't be able to shield very well.

    Consider a neutral carbon atom: it has 6 protons and 6 electrons (2 1s electrons, 2 2s electrons, and 2 2p electrons). If I add a new electron to make a C- anion, the new electron that I'm adding will think that the atom has a charge of around +0.6 because each of the 2p electrons that are already there can only shield another 2p electron from about .7 units of charge. But if I want to add an electron to a F atom to make F-, now my additional electron will see a charge of something like +1.5, since there are already 5 2p electrons present that each allow +0.3 charge to "bleed through" their coverage of the nucleus. If I want to add another electron to my F-, now I will have to add a 3s electron, and the 2p electrons that are already there will shield the 3s electron much better than they can shield other 2p electrons. So the first extra electron that you add to F will see a charge of around +1.5, while the second will see a charge close to -1.

    That is the main reason why atoms are more stable if they can get to 8 electrons to make an octet; so long as you are filling up a partly-filled p orbital, positive charge from the nucleus will be able to get through to attract the extra electrons. Once you have filled the p orbital completely, you now have to add to the next level s orbital, to which very little extra charge from the nucleus can get through. There are also a few issues with electrons being lower in energy if there are a lot of other electrons around with the samle n, l, and Ms values that contribute to the octet rule, but it mainly has to do with charge and charge shielding.
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