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Thread: expline why we write so and so?

  1. #1 expline why we write so and so? 
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    1.why we write Al2O3

    but when alminium are alone we write it like so AL3+ BUT WHY, can somebody explaine??


    2. and Na2O we write so but why? and we it is self we write it like so Na+ but why and not like Na-? why explaine for me, please?



    Your sincerly Lars from Sweden


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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
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    Al2O3 is the stoichiometry of the neutral oxide produced when aluminium reacts with oxygen, in the course of this reaction electrons are transferred from aluminium to oxygen to produce ions. Each aluminium atom loses three electrons to become Al3+ and each oxygen atom gains two electrons to become O2-. When these combine, to balance the charges 3 oxygen ions (total charge 6-) are needed to balance the positive charge of two Al ions (total charge +6) giving the neutral compound aluminium oxide, Al2O3. Hope this helps.

    Either you have edited your OP or I missed the second part, anyway the answer to the second part is in post #17


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  4. #3  
    Universal Mind John Galt's Avatar
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    Aluminium oxide has two aluminium ions to every three oxygen ions. Thus Al2O3.

    Al3+ indicates that the aluminium ion typically has a +3 charge, since it has lost three electrons from its outermost shell.

    Ooops. Cross posted with pHDemon.
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  5. #4  
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    Quote Originally Posted by John Galt View Post
    Aluminium oxide has two aluminium ions to every three oxygen ions. Thus Al2O3.

    Al3+ indicates that the aluminium ion typically has a +3 charge, since it has lost three electrons from its outermost shell.

    Ooops. Cross posted with pHDemon.


    John explaine more why it has lost it?
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  6. #5  
    Bullshit Intolerant PhDemon's Avatar
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    Atoms lose/transfer electrons when it is energetically favourable for them to do so. The energetics of this reaction are covered in the video below:

    Y14 Born Haber Cycle for Al2O3 - YouTube
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  7. #6  
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    Quote Originally Posted by PhDemon View Post
    Al2O3 is the stoichiometry of the neutral oxide produced when aluminium reacts with oxygen, in the course of this reaction electrons are transferred from aluminium to oxygen to produce ions. Each aluminium atom loses three electrons to become Al3+ and each oxygen atom gains two electrons to become O2-. When these combine, to balance the charges 3 oxygen ions (total charge 6-) are needed to balance the positive charge of two Al ions (total charge +6) giving the neutral compound aluminium oxide, Al2O3. Hope this helps.
    but bhow much electron has the aluminum from the first?
    and how much does elextron oxygen has from the first ?
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  8. #7  
    Bullshit Intolerant PhDemon's Avatar
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    I'm not sure what you are asking here, but if you look at the electronic configuration of aluminium you will see it has three valence electrons which can be lost for a relatively small input of energy (ionisation energy), if you look at the electronic configuration of oxygen you will see it has two electrons less than a noble gas configuration and so will readily accept two electrons to form the more stable outer shell (electron affinity). The role these factors play, along with the lattice enthalpy of the oxide are detailed in the video I linked to above.
    Last edited by PhDemon; April 22nd, 2014 at 02:48 PM. Reason: typo
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  9. #8  
    Bullshit Intolerant PhDemon's Avatar
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    I hope lars doesn't mind but he sent me a message asking why Al only loses three electrons and in case any other readers are wondering I'll answer here.

    Al has three electrons in its valence shell, the configuration is [Ne] 3s2 3p1, the 3p and 3s electrons are lost relatively easily as can be seen from the ionisation energies in the link below:

    https://www.webelements.com/aluminium/atoms.html

    you can see the first, second and third electrons are lost with only small (less than 3000 kJ/mol) energy input required. To remove a fourth electron would require removing an electron from a filled lower energy shell and this takes a lot more energy (~12000 kJ/mol, almost 4 times higher), there are many chemical processes that can easily provide the modest energy barrier required to make Al lose three electrons to form a lower energy compound but none that can provide the very high energy cost required for a fourth or subsequent electron to be lost. This is why Al invariably loses three electrons in its chemical reactions.
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  10. #9  
    Administrator KALSTER's Avatar
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    Also, some elements have two favourable ions, like Fe3+ and Fe2+.

    Some of the common ones:



    Or a more comprehensible one (pdf): http://www.google.co.za/url?sa=t&rct...XEmrMWDW-oyPmQ
    lars_1900 likes this.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
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  11. #10  
    Universal Mind John Galt's Avatar
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    Correct me if I am wrong, but it loses these electrons so readily that aluminium oxidises in air very rapidly. This produces a thin layer of aluminium oxide (think rust) on the surface that protects the aluminium from further oxidation.
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  12. #11  
    Bullshit Intolerant PhDemon's Avatar
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    Quote Originally Posted by John Galt View Post
    Correct me if I am wrong, but it loses these electrons so readily that aluminium oxidises in air very rapidly. This produces a thin layer of aluminium oxide (think rust) on the surface that protects the aluminium from further oxidation.
    This is true, any aluminium that is exposed to air has a thin layer of the oxide coating the metal, if you use Al in the lab you often scrub it with wire wool to remove the oxide coating.
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  13. #12  
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    This property of Aluminium prevented its use for some time, until a way to extract it in usable form was discovered.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
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  14. #13  
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    so far i i with you but..........

    but this:
    When these combine, to balance the charges 3 oxygen ions (total charge 6-) are needed to balance the positive charge of two Al ions (total charge +6) giving the neutral compound aluminium oxide, Al2O3.


    i am lost again, can you be good and expaline it in very very easy english!
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  15. #14  
    Bullshit Intolerant PhDemon's Avatar
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    OK, when the reaction occurs you have some aluminium ions which have a charge of +3 and some oxygen ions that have a charge of -2.

    From these you want to make a neutral compound that has no charge and forms a stable crystal or lattice.

    The easiest way for this to happen is for two aluminium ions (each with a charge of +3) to be associated with three oxygen atoms (each with a charge of -2 ).

    The total charge is then (2 x +3) + (3 x -2) = 0
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  16. #15  
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    can somebody explaine this one (the last one)

    when Na meet O what happend????
    explaine in the way we has done in ABOVE!
    Last edited by lars_1900; April 22nd, 2014 at 10:39 AM.
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  17. #16  
    Bullshit Intolerant PhDemon's Avatar
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    As I said in the PM, Si tends not to form ions as it is mid-table in the electronegativity series, it forms covalent bonds as this is more energetically favourable than losing or gaining electrons. The link below may help you:

    Covalent Bonds vs Ionic Bonds - Difference and Comparison | Diffen
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  18. #17  
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    Quote Originally Posted by lars_1900 View Post
    can somebody explaine this one (the last one)

    when Na meet O what happend????
    explaine in the way we has done in ABOVE!
    OK, look at the electronic configuration of sodium: Ne 3s1

    It has one electron in it's valence shell which is easily lost to produce Na+, losing a second electron would require removing an electron from a filled shell which requires a lot more energy as shown in the ionisation energies:

    https://www.webelements.com/sodium/atoms.html

    oxygen as before will gain two electrons to form O2- so we have a mixture of Na+ and O2- ions formed. The neutral, stable oxide formed by these ions is Na2O as two singly charged Na+ ions balance the charge on one O2- ion.
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