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Thread: Melting/Boiling points

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    Melting/Boiling points

    Hi, why do melting and boiling points of a compound depend on its molecular mass?

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    Re: Melting/Boiling points

    if its a non-polar substance, because the greater the molecular mass, the stronger the dispersion forces. Stronger intermolecular forces mean it is harder to break up 2 molecules, and thus it has a higher melting nd boiling point.

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    Re: Melting/Boiling points

    What if it's polar?

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    Re: Melting/Boiling points

    Quote Originally Posted by Pwnage101 View Post
    if its a non-polar substance, because the greater the molecular mass, the stronger the dispersion forces. Stronger intermolecular forces mean it is harder to break up 2 molecules, and thus it has a higher melting nd boiling point.
    o i thought that all molecules, polar and non polar had dispersion forces according to their size and mass, thats y we can get all elements as a solid because there are dispersion forces present in all molecular bonds.
    the non-polar substances have the dipole-dipole bonds requiring more energy to break these bonds. (lol im hesitant about questioning you because i saw what ur HSC results were =s)

    so to op this i what i think.
    as mass and size of the molecules increase they create stonger dispersion forces, requiring larger amounts of energy to break these bonds.

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    Re: Melting/Boiling points

    The way I understand it, the larger the molecule, the more electrons that are displaced to create the temporary dipole and hence the greater the force between molecules.

    In order for a substance to melt and then boil, intermolecular forces must be overcome. Thus, the stronger the intermolecular forces, the higher the melting/boiling points.

    Consequently, the larger the molecule, the higher the melting and boiling points of that substance.

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    Re: Melting/Boiling points

    Quote Originally Posted by shady145 View Post
    o i thought that all molecules, polar and non polar had dispersion forces according to their size and mass, thats y we can get all elements as a solid because there are dispersion forces present in all molecular bonds.
    the non-polar substances have the dipole-dipole bonds requiring more energy to break these bonds. (lol im hesitant about questioning you because i saw what ur HSC results were =s)

    so to op this i what i think.
    as mass and size of the molecules increase they create stonger dispersion forces, requiring larger amounts of energy to break these bonds.
    I think what Pwnage101 was trying to say was that since non-polar molecules only have dispersion forces and nothing else as their intermolecular bonds. That is why the higher the molecular mass the higher the molecular mass the higher the melting/boiling point. Polar substances also have dispersion forces but it is more difficult to find the melting/boiling point as you have to take into account the differences in electronegativity.
    cracker

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