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    Why does Magnesium Oxide have a much higher melting point and lattice energy than Sodium chloride?

    Also, why is sodium chloride soluble in water and magnesium oxide not?

    Thanks =)
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    (Original post by fomo)
    Why does Magnesium Oxide have a much higher melting point and lattice energy than Sodium chloride?
    They both have ionic bonding, but MgO has two donated electrons [Mg(2+)] as opposed to NaCl which has only donated one [Na(+)], so it's doubly charged. You can see in the periodic table as Na is in group 1 and Mg is in group 2, for example. So attraction between Mg and O is stronger and thus more energy (high temperature) is required to overcome the greater attractive force.

    A bit vague, but it's been a while.
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    (Original post by fomo)
    Why does Magnesium Oxide have a much higher melting point and lattice energy than Sodium chloride?

    Also, why is sodium chloride soluble in water and magnesium oxide not?

    Thanks =)
    Mg2+ has higher charge than Na+.

    O2- has higher charge than Cl-.

    Higher charges mean stronger lattice energy, hence the strength of the bonds between them are stronger, difficult to break, hence higher melting/boiling points.

    Dissolving means weakening the bonds and incorporate them with water molecule(forming new bonds), since the lattice energy of NaCl is smaller than that of MgO, therefore it is more soluble than MgO.

    NB, when i say lower value for LE, i know that all LE are negative, so i am just talking about their numerical values, make life easier.
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    (Original post by shengoc)
    Mg2+ has higher charge than Na+.

    O2- has higher charge than Cl-.

    Higher charges mean stronger lattice energy, hence the strength of the bonds between them are stronger, difficult to break, hence higher melting/boiling points.

    Dissolving means weakening the bonds and incorporate them with water molecule(forming new bonds), since the lattice energy of NaCl is smaller than that of MgO, therefore it is more soluble than MgO.

    NB, when i say lower value for LE, i know that all LE are negative, so i am just talking about their numerical values, make life easier.
    I'd echo what the above has put but just add the phrase in bold. Sometimes exam mark schemes can be very specific and they dock a mark by not adding one particular word/phrase.

    The electrostatic attraction between higher charges are stronger, hence the strength of the bonds between them are stronger, more energy is required to break them (rather than just stating that they're difficult to break), hence higher melting/boiling points.

    Just me being pedantic :p: But exam technique is just as important as knowledge at A-level.

    My 2p worth...
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    (Original post by Kinkerz)
    I'd echo what the above has put but just add the phrase in bold. Sometimes exam mark schemes can be very specific and they dock a mark by not adding one particular word/phrase.

    The electrostatic attraction between higher charges are stronger, hence the strength of the bonds between them are stronger, more energy is required to break them (rather than just stating that they're difficult to break), hence higher melting/boiling points.

    Just me being pedantic :p: But exam technique is just as important as knowledge at A-level.

    My 2p worth...
    True, uni life is so much better, you write whatever that makes sense, and that could earn you marks already. I think as long as you get the essential bits, you would show an understanding and from your answers, any sensible examiners would understand that.

    Not trying to say you are wrong, or whatsoever, anyway, all the best.
 
 
 
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