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    When naming alkenes with a substituent group, how do you identify the position of each substituent? I mean, where do you start counting? In my book it says 'the numbering is done from the end of the carbon chain that gives the lowest number for the substituent group'. I don't understand the wording of that.

    Also, about electron affinities. In a graph of first electron affinities of the elements in the second period, beryllium is lower than lithium, and nitrogen is lower than carbon. Why is this? My book says 'The dip at beryllium occurs because the added electron goes into an already occupied 2s-orbital'. Surely this would happen in lithium, not beryllium, as the electron configuration of lithium is [He] 2s1?

    Thanks
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    Okay with the numbering, if you have this molecule:
    H3C-CH2Br-CH2-CH2-CH3.

    You could either number it as 2-bromopentane (bromine on the second carbon) or as 4-bromopentane (bromine on the fourth carbon). Its real name is 2-bromopentane because it gives the lower number, and that is what your definition means. They are actually just the same molecule, so you use the lower number

    Electron Affinity is ADDing an electron to a neutral atom, so adding an electron to Lithium makes it more stable because it then has a spin pair of electrons (more stable than one unpaired electron). When you add an electron to Beryllium which already had a spin pair, it has an unpaired electron in its p-orbital, and this destabilies the molecule, so its electron affinity is lower.
    It's a similar story for nitrogen, as a neutral molecules it has a half shel of unpaired electrons which is relatively stable, adding an electron disrupts this and so electron affinity is lower.

    Hope this helps, explaining isn't my best skill!
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    http://www.creative-chemistry.org.uk...ositional.htm#
    ^ In butan-2-ol here if you count the carbons from the left it becomes butan-3-ol. But if you count the carbons from the right it becomes butan-2-ol. As 2 is smaller than 3 you should always count from the right.
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    I get it now, thanks
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    (Original post by - skyhigh -)
    http://www.creative-chemistry.org.uk...ositional.htm#
    ^ In butan-2-ol here if you count the carbons from the left it becomes butan-3-ol. But if you count the carbons from the right it becomes butan-2-ol. As 2 is smaller than 3 you should always count from the right.
    You don't always count from the right, just from whichever side that you get a lower number :p:
    But if you meant just your example, then yeah
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    Yep I meant the example lol :p:
 
 
 
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