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Electronegativity

Discussion in 'MCAT Study Question Q&A' started by cwfergus, Jun 3, 2008.

  1. cwfergus

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    Hey guys, is there any special way you remember what the electronegativity of the elements are so if asked a bonding question?

    such as like how do you know waht Carbon or Nitrogen or Phosphorous is? do you memorize it?
     
  2. Kaustikos

    Kaustikos Archerize It
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    You don't need to memorize the values specifically, just know the trends on the periodic table (ie - larger electronegativity top right and lower bottom left). This all coincides with all the trends in the periodic table (size, electron affinity, effective charge, ionization energy)

    Figuring out if they'll bond ionically is determined by subtracting the values of the two and seeing if the difference is, I believe, larger than 1.5. So, in short, Fluorine would literally bear hug the hell out of Francium and never let it go.
     
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    cwfergus

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    Yeah exactly, those have great affinity for eachother, but what if its reallly close, i dont know... like i dont have an electronegativity chart with me, but just say the difference is 1.3 or something, but you dont KNOW that becasue you arent given it. do you just make a guess and say its got a polar covalent bond? i dont konw
     
  4. chemnerd31

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    You have your trends mostly right but to exactly.

    Electronegativity: increases left to right bottom to top
    Atomic Size: increases right to left and top to bottom
    Ionization Energy: increases left to right and bottom to top
    Electron Affinity: not great correplation from left to right but a slight increase sometimes from bottom to top
     
  5. Kaustikos

    Kaustikos Archerize It
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    My logic in those situations is to just use the golden rule used in 8th grade. The metals and nonmetals make ionic bonds. OTherwise; it's covalent/non-ionic.

    But in your situation, the designation of ionic vs polar covalent isn't made just by that electronegativity difference because books say "around 1.5". Some ionic bonds are actually weaker than that. I would say that if you feel the bond isn't ionic, then saying polar covalent wouldn't hurt. Though I seriously doubt the MCAT would ask for you to do that. The last question I can recall dealing with this gave a chart and asked you to picka compound that was the most electronegative. The only trick was that one of the choices had two compounds with one not being in the chart provided leading one to think that 'Oh, not on the list, so it's not counted' when it was actually the right answer.
     
  6. auroraboy

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    Here's a mnemonic to remember electro negativity of most common elements you see on MCAT:

    "fawn-cull-brish" corresponding to FON-Cl-BrISCH

    Electronegativity follows this order..

    Florine>Oxygen>Nitrogen>Chlorine>Bromine>Iodine>Sulphur>Carbon>Hyrdongen

    Hope this helps!
     
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    cwfergus

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    FON CL BRISCH

    so Flourine has the HIGHEST ENT while Hydrogen has around a 2.2 or so.
    sooo flourine and hydrogen would form an ionic bond, but carbon and down would be covalent? (whether polar or nonpolar)
     
  8. auroraboy

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    Essentially, just carbon and hydrogen would form covalent bond in this list...all other elements would from ionic bond with hydrogen.
     
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