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    does the presence of a lone pair in a compound always make it polar ?? and why
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    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.
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    (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.
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    (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??
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    (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
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    (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.
 
 
 
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