IGCSE Chemistry 0620/21/O/N/21 Q22

Question

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22 Group VII elements show trends in their physical properties going down the group.

element      X       Y       Z
chlorine  –101  –34  0.003
bromine  –7       59    3.1
iodine       114   184    4.9

Which row shows the missing headings for the properties in the table?
X                                     Y                                        Z
A    density in g / cm3      boiling point in °C       melting point in °C
B     melting point in °C    boiling point in °C        density in g / cm3
C      boiling point in °C     density in g / cm3      melting point in °C
D      boiling point in °C     melting point in °C      density in g / cm3

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Answer ( 1 )

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    2022-05-11T22:27:30+08:00

    Intermolecular force is considered when discussing melting and boiling points. (Consider bonds between atoms of molecule e.g. ionic bonds, covalent bonds, when discussing reactivity.)

    A factor affecting intermolecular force is size of atom (down the same group of periodic table).

    Size of atoms of Group VII elements increases as chlorine, bromine, iodine.

    Hence, intermolecular force (Van der Waals) involving these atoms increases as chlorine, bromine, iodine.

    Same order goes to boiling and melting points.

     

    Density is based on mass per unit volume of atoms. Atomic mass of atoms in Group VII elements increases as chlorine, bromine, iodine. Hence, density increases in the same order.

     

    To determine whether X or Y is melting or boiling point, you can consider this:

    Chlorine is gas at room temperature (25 degree Celsius). Hence, its boiling point should be lower than that. If options are -101 and -34, the lower temperature should be the melting point (higher should be boiling point.)

    Ans: B

     

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