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  • Electron arrangement

    Hi, please can someone help me. Currently on module 15 pharmaceutical science 2, npa technician course. My book tells me that the atom shells are arranged as 2,8,16 but then when I've been looking else where is shows 2,8,8. So for example i had to answer the arrangement for calcium. Going on what my book is teaching me i went for 2,8,10 as it says the 3rd shell can hold up to 18. So why is the answer 2,8,8,2?? Why is the third shell not holding all remaining electrons? I hae tried to search online but am now becoming confused. Thanks

  • #2
    Hi. Haven't thought about this in decades and had forgotten most of it. Thanks for the non pharmacy-grind question! The world is such an amazing place...much better than sorting out surgeries that can't write a CD Rx properly or trying to explain to a palliative care nurse that I can't just give a long nozzle enema of the same substance without a new script as it costs an extra £20 each for no reason I can begin to explain.

    Someone else will probably explain better but I'll try and help. It has to do with the energy levels for each shell. The electrons fill up as per the diagram below (note that 4s2 fills up before 3d10). Hence, if you fill up calcium's 20 electrons according to the chart you get an answer of 2,8,8,2.

    The following link has a good visual explanation. https://antranik.org/electrons-shells-and-orbitals/

    Shells (PQ #)


    As you add shells, they move further away from the nucleus but each shells moves less further away with each subsequent shell. The shortest wavelength has the highest energy. And the valence e- are the ones in the outer shell.

    http://antranik.org/wp-content/uploa...figuration.jpg

    There is an energy overlap between 3p6 and 4s2. 4s has less energy than 3d:

    http://antranik.org/wp-content/uploa...-in-orbits.gif


    Good luck!
    Last edited by Locum X; 1st, May 2018, 08:48 PM. Reason: Fat fingers

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    • #3
      Originally posted by JO_85 View Post
      Hi, please can someone help me. Currently on module 15 pharmaceutical science 2, npa technician course. My book tells me that the atom shells are arranged as 2,8,16 but then when I've been looking else where is shows 2,8,8. So for example i had to answer the arrangement for calcium. Going on what my book is teaching me i went for 2,8,10 as it says the 3rd shell can hold up to 18. So why is the answer 2,8,8,2?? Why is the third shell not holding all remaining electrons? I hae tried to search online but am now becoming confused. Thanks
      Depends how in depth you go.

      So there are shells and subshells.

      The shells are 2, 8, 18.

      The subshells that make these up are

      1s (2)
      2s 2p (2 + 6)
      3s 3p 3d (2 + 6 + 10)

      If you want to know where the numbers come from it's quantum mechanics.

      The shells are cumulative. So the electron configuration of Calcium is 1s2-2s2-2p6-3s2-3p6-4s2

      However calcium is either a really dumb ass example to choose in the book or a clever one to make you think if you go that far, because if you go into a deeper level in A-level chemistry or quantum mechanics, it's electron configuration isn't what you'd expect. The 4s shell fills up before the 3d shell! Cr and Cu also have configurations a GCSE student might find odd.

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      • #4
        What possible practical relevance is this to a technician’s role?

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        • #5
          Thanks all. My book does not cover subshells at all or even mentions them so kind of makes it hard to know which ones are 8 or 18! It literally just says the third shell holds 18, hence me assuming there would be 10 electrons in the 3rd shell. Am i right in thinking the first 20 elements all use the 2,8,8, sequence? Thanks again

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          • #6
            Originally posted by hibernia View Post
            What possible practical relevance is this to a technician’s role?
            I have no idea, even my pharmacist said she would need to go back to her books to know if im answering correctly!

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            • #7
              I have said many times that NPA course not fit for purpose. I did all this at Grammar School nearly 70 years ago and forgotten most. Did it again at uni with Quantum theory and that was over 60 years ago. Mentioned again when I looked at how LEDs work some years ago. However, unnecessary for a technician in my view. Perhaps someone who approves of NPA course could explain why considered important.
              johnep

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              • #8
                Originally posted by JO_85 View Post
                Thanks all. My book does not cover subshells at all or even mentions them so kind of mAm i right in thinking the first 20 elements all use the 2,8,8, sequence? Thanks again
                The 3d subshell has 10 elements.

                The first 18 elements follow what you say and so in books it says things like [Ar]4s^2

                Even the

                This means electronic configuration of argon a noble gas with with a full shell and add on two for Calcium.

                Is there a periodic table in the book? It makes more sense as you can see the subgroups.

                knowing about this stuff is useful for periodicity but cannot see relevance for tech. To understand why the madelung rule breaks in certain caes requires a course in quantum theory!

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                • #9
                  Originally posted by mcitr View Post

                  The 3d subshell has 10 elements.

                  The first 18 elements follow what you say and so in books it says things like [Ar]4s^2

                  Even the

                  This means electronic configuration of argon a noble gas with with a full shell and add on two for Calcium.

                  Is there a periodic table in the book? It makes more sense as you can see the subgroups.

                  knowing about this stuff is useful for periodicity but cannot see relevance for tech. To understand why the madelung rule breaks in certain caes requires a course in quantum theory!
                  Yes there is a periodic table, thats how i knew my answer for calcium was wrong as i knew it should of ended with a 2. Really don't understand why the course teaches you the third holds up to 18 but in no way then explains anything to do with sub shells. I thought i fully understood this module and now im confused again. It clearly doesn't want me to go into sub shell territory as it doesn't mention it at all. But then has examples of some that hold 8 in its 3rd shell with a forth shell and some that hold more than 8 in the 3rd with no explanation. I 100% never expect to use this again once this module is complete but unfortunately it has an exam so have to try and understand it in some way.

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                  • #10
                    Originally posted by hibernia View Post
                    What possible practical relevance is this to a technician’s role?
                    Yes. My pharmacist had to hunt out his sons chemistry book. When that proved fruitless, I had help from his son!!!!!!!

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