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Chemistry Gcse Qs watch

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    1. Why do ionic substances have high melting and boiling points?

    2. How are igneous rocks formed?
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    (Original post by sloaney87)
    1. Why do ionic substances have high melting and boiling points?

    2. How are igneous rocks formed?
    1) because they have strong bonds between the particles that make up the substance. which require alot of energy to be broken up. maybe

    2) cooling and crystallisation of magma forming randomly arranged crystals
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    (Original post by sloaney87)
    1. Why do ionic substances have high melting and boiling points?

    2. How are igneous rocks formed?

    1. Very strong chemical bonds between all the ions

    2. Magma cooling.
    Extrusive igneous rocks are ones which cooled outside the earth, very quickly forming small crystals e.g Basalt
    Intrusive are cooled inside the earth, cool slowly forming large crystals e.g Granite.
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    (Original post by sloaney87)
    1. Why do ionic substances have high melting and boiling points?

    2. How are igneous rocks formed?
    from the syllabus:
    1) ionic compounds form regular structures (giant ionic lattices) in which the strong forces between oppositely charged ions result in these compounds having high boiling and melting points.

    2) syllabus doesnt say how igneous rocks are formed but kieshaxx is right
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    according to our chem teacher the rock stuff aint on the AQA syllabus this year. But if it does come up its fairly simple, only a page or so of learning

    I always mess up the Q on why more branched isomers have lower boiling points. Can anybody give me an ideal answer to memorise ?

    Chris

    (Original post by Jingo)
    according to our chem teacher the rock stuff aint on the AQA syllabus this year. But if it does come up its fairly simple, only a page or so of learning

    I always mess up the Q on why more branched isomers have lower boiling points. Can anybody give me an ideal answer to memorise ?

    Chris
    The bonds that must be broken for a molecular substance to boil are the ones between the molecules. Some of these (Van der Waals forces - but I don't think you need this for GCSE) are strongest when the molecules are closest together.

    A molecule that is branched and has bits sticking out everywhere cannot "pack" together with its fellow molecules as easily as one that is primarily long and thin (i.e. linear) - like tesselations in maths.

    Therefore the branched molecules can't get as close to each other, so these forces that depend on (partly) on distance are weaker. The weaker bonds require less energy to break so the boiling point is lower.

    This isn't intended as a model answer but to help you understand it

    rosie
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    yeah i understand it now. Ta

    Ill write out a memorisable way of putting it though, that mini-essay ill neva rememba. lol

    chris
 
 
 

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