Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    12
    ReputationRep:
    does the presence of a lone pair in a compound always make it polar ?? and why
    Offline

    8
    ReputationRep:
    Generally speaking yes, a lone pair would make a compound polar.
    This is because you have a region of space (sub-orbital) that is taken up by 2 electrons. That makes that area of space very negatively charged, we call this an area of high electron density. So if one end of the molecule was very negatively charged and the other end wasn't (i.e. the other end of the molecule doesn't also have a lone pair) there would be a charge difference across the molecule. If this charge difference is big enough we call the molecule a polar molecule.

    Hope that helps.
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by NoorL)
    does the presence of a lone pair in a compound always make it polar ?? and why
    Not necessarily, if the molecule is symmetrical such as carbon dioxide. Each oxygen has two lone pairs but the molecule as a whole is non-polar as the individual dipoles cancel out.

    The same is true of sulfur trioxide, but not sulfur dioxide.
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by Dannyboy2015)
    Generally speaking yes, a lone pair would make a compound polar.
    This is because you have a region of space (sub-orbital) that is taken up by 2 electrons. That makes that area of space very negatively charged, we call this an area of high electron density. So if one end of the molecule was very negatively charged and the other end wasn't (i.e. the other end of the molecule doesn't also have a lone pair) there would be a charge difference across the molecule. If this charge difference is big enough we call the molecule a polar molecule.

    Hope that helps.
    thanks a lot! also what is meant by a lone pair is directional??
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by charco)
    Not necessarily, if the molecule is symmetrical such as carbon dioxide. Each oxygen has two lone pairs but the molecule as a whole is non-polar as the individual dipoles cancel out.

    The same is true of sulfur trioxide, but not sulfur dioxide.
    so u mean that if there are two lone pairs opposite to each other they cancel out and therefore the molecule becomes nonpolar............. and also in h2o there is onlu one lone pair so it makes it polar right??

    one more thing.. what is meant by a lone pair is directional
    thank u very much xx
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by NoorL)
    so u mean that if there are two lone pairs opposite to each other they cancel out and therefore the molecule becomes nonpolar............. and also in h2o there is onlu one lone pair so it makes it polar right??

    one more thing.. what is meant by a lone pair is directional
    thank u very much xx
    Water has two lone pairs as part of a tetrahedrally arranged electron domain structure..

    Dipoles exist between atoms of different electronegativity (forget lone pairs). Dipoles are vector quantities, i.e. they have both magnitude and direction.

    Individual dipoles can be resolved into xyz directions (three dimensions) using the law of parallelograms.

    If all of the resolved vectors cancel out then the structure overall is non-polar.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Would you like to hibernate through the winter months?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.