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Homework Help: Introductionairy(!) chemistry problem, SO4

  1. May 5, 2016 #1
    1. The problem statement, all variables and given/known data
    Ok, I recently started studying again after a 1.5 year break to pursue other things. I am trying to plow through this chemistry course, and I remember this forum where I basically got through my entire physics course because of the help of this forum which I greatly appreciate.

    Ok, this is very simple but I have a hard time understanding this. Why does sulphate have 4 oxygens and -2 charge. I have a series of questions in my course, and among it, it said to write the formula for Aluminium chloride for example, which I understand is AlCl3 since Al has +3 charge and Cl has -1 so there has to be 3 of Cl to even things out, right? But this problem with writing sodium sulphate has me confused. I see that Sulfur and Oxygen is combined to make sulphur, but why on earth does it have to be 4 oxygens and 1 Sulfur? In my mind both needs 2e- to be happy, so why can't they just share it? If one atom of Sulfur shares with 1 atom of Oxygen, wouldn't they be happy? They could share one electron each and be content?

    Do I just have to learn in my head that sulphate has the formula So42-? Likewise nitrate has NO3?

    I am sorry, I am just massively confused by this.



    PS: If this is not worthy to be a thread I apologize, and if it is in the wrong place, please remove.
  2. jcsd
  3. May 5, 2016 #2


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    Staff Emeritus
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    Homework Helper

    Certain elements, like sulfur and nitrogen, have multiple valence states. With sulfur, you can have one sulfur atom oxidized to SO2, SO3, or SO4, depending on certain conditions:


    Similarly, nitrogen can oxidize to more than a dozen different compounds:


    Elements like the alkali metals or the halogens generally have only one valence state. Their chemistry is much simpler to master.
  4. May 5, 2016 #3


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    Staff: Mentor

    At the beginning just remembering these formulas is the simplest approach. Later it is still the simplest approach - even once you can explain why the formula is SO42- it is easier to remember it, than to "derive" the correct formula from the first principles.

    And beware - not NO3, but NO3-. These charges are pretty important here.
  5. May 5, 2016 #4
    Thank you Steamking, and Borek for your responses. I will take your advice Borek and just remember the formulas for sulphate and nitrate, and thank you for the correction of the charge. I forgot to put it in.

    It's fun to see you again Borek, if I remember correctly you helped me 2 years ago also, it is good to see this forum still thriving.
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