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    Hi

    I've just been doing polar and non-polar molecules in my chemistry class, and I dont really get it.

    How would you work out if a molecule is polar or non-polar? I know its to do with the electronegativity and geometry of the molecules, but how would I determine it using that information?

    It'd be great if someone could explain that to me and possibly illustrate it with a few examples.

    Thanks
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    Something has a polar bond when there is a charge difference, for the molecule to be polar there must be an imbalance across the whole molecule (a lack of symmetry) . A few examples;

    O=O is not polar because the bonds are non-polar (same electronegativities) and the molecule is linear

    CO is polar be because there is a significant difference in the electronegativities of C and O, since there are only two atoms CO must be polar

    O=C=O has polar bonds, but is not polar itself because of the symmetry (the polarity is equal but opposite in direction)

    A few more examples;

    H3C-CH2-CH3 (propane) has two different atoms types but have very similar electronegativities so reamins largley non-polar

    NH3 has 3 polar N-H bonds and due to its shape - trigonal pyramidal - a lone pair of electrons occupies one of the corners of the tetrahedral so we have polar N-H bonds pointing in one direction and the lone pair pointing in the opposite direction - charge imbalance

    H2O has two polar O-H bonds, its shape (bent) means that these dipoles don't cancel each other out in the fashion of CO2 and so water is polar

    Can you tell if these are polar?

    SO3 (easy)
    propanone (medium)
    O3 (hard)
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    (Original post by EierVonSatan)
    Something has a polar bond when there is a charge difference, for the molecule to be polar there must be an imbalance across the whole molecule (a lack of symmetry) . A few examples;

    O=O is not polar because the bonds are non-polar (same electronegativities) and the molecule is linear

    CO is polar be because there is a significant difference in the electronegativities of C and O, since there are only two atoms CO must be polar

    O=C=O has polar bonds, but is not polar itself because of the symmetry (the polarity is equal but opposite in direction)

    A few more examples;

    H3C-CH2-CH3 (propane) has two different atoms types but have very similar electronegativities so reamins largley non-polar

    NH3 has 3 polar N-H bonds and due to its shape - trigonal pyramidal - a lone pair of electrons occupies one of the corners of the tetrahedral so we have polar N-H bonds pointing in one direction and the lone pair pointing in the opposite direction - charge imbalance

    H2O has two polar O-H bonds, its shape (bent) means that these dipoles don't cancel each other out in the fashion of CO2 and so water is polar

    Can you tell if these are polar?

    SO3 (easy)
    propanone (medium)
    O3 (hard)
    So to answer the question when predicting polarity, you have to draw the shape? any shape that is distorted is polar, simple? :dontknow:
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    (Original post by Barry Chuckle)
    So to answer the question when predicting polarity, you have to draw the shape? any shape that is distorted is polar, simple? :dontknow:
    Well you do have to know the structure of the molecule - but not all distorted things are polar...
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    Right...thanks a lot EierVonSatan! Also, nice signature...
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    Not sure myself on the o3 - should emphasis be placed on the delocalization of the electrons? I have heard that resonance structures give accurate representations for this molecule, but have always believed there to be no charge imbalance.
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    (Original post by DeanK2)
    Not sure myself on the o3 - should emphasis be placed on the delocalization of the electrons? I have heard that resonance structures give accurate representations for this molecule, but have always believed there to be no charge imbalance.
    it's a bent molecule with the electron density focused on the outer oxygens, and so is polar (draw out out the resonance forms and you find the positive charge always resides on the centre oxygen)
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    Hey, could you please give me a clear explanation to why hydrogen bonds are called hydrogen bonds or what are hydrogen bonds and carbon bonds?
    Why do we call H2O molecule bonding a hydrogen bond? as if oxygen is also present there, I know the electro negativity of oxygen is more than hydrogen and hydrogen is electron donor in H2O molecule but in CH4 carbon makes 4 covalent bond with hydrogen and we call it carbon bond. What are the basics? Please guide me:confused:
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    (Original post by Fatimaltaf)
    Hey, could you please give me a clear explanation to why hydrogen bonds are called hydrogen bonds or what are hydrogen bonds and carbon bonds?
    Why do we call H2O molecule bonding a hydrogen bond? as if oxygen is also present there, I know the electro negativity of oxygen is more than hydrogen and hydrogen is electron donor in H2O molecule but in CH4 carbon makes 4 covalent bond with hydrogen and we call it carbon bond. What are the basics? Please guide me:confused:
    The term "hydrogen bond" is a misnomer, as it is not actually a bond, just a temporary electromagnetic attraction. It is simply the attraction of the hydrogen molecule to a strongly electronegative atom, such as fluorine or oxygen, and electrons are not shared, like they are in covalent bonding. Since there is an oxygen molecule within a water molecule, a hydrogen bond also exists. A hydrogen bond is stronger than the van der Waals force, but weaker than covalent/ionic bonds.

    As for carbon, it is positively charged when it is in its ionic form, and therefore a hydrogen bond cannot exist in this scenario. In this case, the carbon and hydrogen actually share electrons, which means that a carbon-hydrogen bond is a covalent bond.

    I hope that helps somewhat.
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    (Original post by Ezraeil)
    The term "hydrogen bond" is a misnomer, as it is not actually a bond, just a temporary electromagnetic attraction. It is simply the attraction of the hydrogen molecule to a strongly electronegative atom, such as fluorine or oxygen, and electrons are not shared, like they are in covalent bonding. Since there is an oxygen molecule within a water molecule, a hydrogen bond also exists. A hydrogen bond is stronger than the van der Waals force, but weaker than covalent/ionic bonds.

    As for carbon, it is positively charged when it is in its ionic form, and therefore a hydrogen bond cannot exist in this scenario. In this case, the carbon and hydrogen actually share electrons, which means that a carbon-hydrogen bond is a covalent bond.

    I hope that helps somewhat.
    Yup I got it Thank you!
 
 
 
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