9) The Periodic Table: chemical periodicity (2016)

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9 thoughts on “9) The Periodic Table: chemical periodicity (2016)

  1. Hello yet again,my question is :
    acidity of Period 3 oxides increases form left to right due to an increase in oxidation number.(its in my lecturers notes but she didnt explain why is it such}

    Thank you

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    • Hi Pendragon1997.
      Personally, I would never say increase in oxidation number is the reason, but I would say it provides a potential way as to how to memorise the change, although I myself would be very unlikely to use such a method for a number of reasons.
      I would instead say the “level of ionic character of the O” atom is is why the oxide is acidic or alkaline.
      E.g. Na2O. The O is very ionic. (v. low polarisation by the Na), so (O)2- anion in interact strongly with a delta+ H in water when it comes into contact with it. The (O)2- will pull off a proton, forming 2 OH- ions.
      In something like SO2, the O is covalent, it’s attached to the ‘central atom’. Any H that the O may abstract a H from water, cannot form ‘free’ OH- ions, i.e. hydroxide ions, because the O is tethered to the central atom. Also, there is no ‘free’ OH ions left over as was the case when water lost a H+ to Na2O and the water produced an OH- also. The water with covalent oxides was ALSO tethered to the central atom when it formed a bond to the central atom (it’s actually a nucleophilic addition reaction!)

      So really, Its the ionic or covalent nature of the oxide that determines it’s basic/acidic properties.

      Here’s a quick proposed mechanism to illistrate what I’m talking about.

      Hope that helps.

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      • I understand your explanation(need some time to get it) and didnt thought of how H2SO3 forms(only memorize in textbook).

        Anyway,do you have any tips to help me study chemistry and scoring excellently in A-level(taking AS and A2 this year).

        Coincidentally today marks my 19th year of living on Earth and still being dependent of my parents earning to survive until i get a degree plus job.

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  2. found this equation in Advance Study Guide chemistry book:
    Al2O3 + 2NaOH + 3H2O to 2NaAl(OH)4 (sodium aluminate)

    From what i learned,water is always at the right hand side of equation.Have any explanation for it and also about the product formed.

    Thanks

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  3. The oxides can be
    a) basic
    b) amphoteric
    c) acidic
    d) non-reactiove

    Basic oxides react to form basic solutions
    Amphoteric oxides can react with acid or base
    Acidic oxides react with water to form acidic solutions.

    Al2O3 is amphoteric and can react with an acid or a base.
    Similar processes to what I mentioned in my previous comment are happening here, but (I think!) BOTH happen. It’s pretty tricky to show, but essentially, the OH- ions of NaOH (remember the Na and OH- ions are ‘free’ of each other, they aren’t “stuck together” in the presence of water) attacks the Al2+ ions of Al2O3, and the O’s in Al2O3 rips off a proton from water as before.
    It has to be NaOH (probably hot and concentrated, yes??) that starts the attack as Al2O3 doesn’t react with water.

    I’m not sure why you say H2O has to be on the right hand side of the equation. Why would that have to be?

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    • I think my concept is wrong(probably from spm).

      My chem teacher always taught me that an acid and base reaction produces salt and water as products.

      However in this case Al2O3(as acid) and NaOH(base) and H2O forms salt only.Thats why i began asking about.

      Anyway,Thank you for willing to answer my doubts !!!

      Like

      • Acid plus base does give salt plus water, but this memory aid doesn’t apply for absolutely everything. It does apply to your ‘traditional’ acids e.g. HCl(aq), HNO3(aq), CH3COOH(aq) etc with your traditional’ bases, e.g. NaOH(aq), NH3(aq) etc

        Seen the reaction of Na2CO3(aq) i.e. sodium carbonate) and HCl(aq)?
        Na2CO3(aq) + 2HCl(aq) –> 2NaCl + H2O + CO2
        salt + water and CO2 is produced. There wasn’t any mention of CO2 in that statement you learned. The statement you learned is useful, but you just need to know when a little bit extra or something slightly different occurs.

        The acidic oxide isn’t an acid in it’s own right. It doesn’t have a proton that it can donate. So it’s not like the ‘traditional’ acids mentioned beforehand (which do have a proton to donate), hence in the case of the Al equation you gave, no water is produced in the reaction with NaOH.

        By the way, the CIE “red book”, Cann and Hughes on page 192 , uses the value of electro negativity to predict what reaction happens. But it’s more of a memory aid rather than an actual reason as to why it happens (but there is some relationship) and to use it effectively you have to remember it in terms of the numbers, which isn’t so great IMHO.
        I advise my students to use diagrams of period 3 to show the trend (e.g. sketch the ‘row’ of period 3 in your notes, Na2O and MgO are to be coloured blue.The Al2O3 is left white, the SiO2, P4O10, SO2 and Cl2O are coloured red. You can quickly see the trend then and may be able to memorise the ‘shape’ / colour bands as a picture, or you can make up some kind of ‘rhyme’ e.g. “Nam-G” (NaMg)played BASS(base) guitar in the band ‘The Oxides’. Their manager Al, always preferred that they play in the amphitheate….. something like that….. I’m sure you can see what I’m saying there.

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  4. And I wish you a happy birthday. Hope you have a great day.

    One tip to get a good ‘A’ is don’t rely on memorising stuff in chemistry. The course is designed to be something like only about 50% of information needs recall skills.

    Do try and understand it. Yes, it takes some time, and there are some things which are best off memorised, but if you understand it your power of remembering (by understanding) will make things so much easier.

    To understand it, you need to read books which explain things. The modern books are usually quite good at doing it. Do read a few sources. chemguide.co.uk is usually excellent at explaining things in simple and easy to accept & ‘remember’ ways. You doing the AS and A2 exams this summer?

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    • That’s correct,doing AS in may/june and A2 oct/nov.
      I will work hard to achieve my parents dreams(lol) to have a good future in life!!!

      Like

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