? asked in 科學及數學化學 · 1 decade ago

4條chem q

1.點解van der waal's force among molecules大d, b.p會高d??

2.boiling既時候係涉及拆bond定form bond?

3.點解straight-chain alkanes do not show the same smooth increase in m.p. with increasing no. of carbon atomes as they show in their b.p.?

4.點解F2 reactive than Cl2,Br2及I2?


點解你第2題話Bond breaking is involved in boiling.

但第3題又話Boiling does not involve the breaking of solid lattice???

1 Answer

  • 1 decade ago
    Favorite Answer


    The higher the van der Waals' forces between molecules, the higher is the boiling point. This is because more energy is needed to break the van der Waals' forces between molecules. (Refer to answer of Q.2)


    Bond breaking is involved in boiling.

    In boiling, the substance changes from liquid state to gaseous state. In liquid state, the constituent particles (i.e.atoms, molecules or ions) are held together by bonds or binding forces. In gaseous state, there are negligible attractive forces between constituent particles.


    Melting involves the breaking of solid lattice. Alkane chains with even number of carbon atoms packed more closely in the crystalline state. As a result, attractive forces between individual chains are greater and thus melting points are higher.

    Boiling does not involve the breaking of solid lattice, and thus the change of boiling points is smoother.


    F2 is the most reactive among the halogens, because:

    (i) F-F bond strength is abnormally weak, because the repulsive forces between the unshared pairs of electrons on the two F atoms are great due to the small size of F atom.

    (ii) F can form stable lattice of ionic compounds with very small F- ions.

    (iii) F can form strong covalent bonds with the atoms of other elements.

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