f5Chem intermolecular forcex3

1.
(a)
The water beam is deflected by the charged rod, as the charged rod attract thewater beam.

(b)
The water beam is NOT deflected/attracted by the charged rod.
Water molecule is polar. The charged rod can attract the ends of unlike charge ofthe water molecules, and this causes the water beam to be deflected.
Tetrachloromethane molecule is non-polar. The charged rod CANNOT attract thetetrachloromethane molecules at all.

(c)
The electronegativity of H is lower than that of S. The difference in theirelectronegativities makes the electron clouds of the bond pair electrons NOTevenly distributed between the two bonding atoms, H and S, but are more closeto the S atom. Therefore, H-S bond is polar.
H­2S is a V-shaped molecule. The sum of dipole moments of the twopolar H-S bonds in H2S molecule is non-zero. Therefore, H2Smolecule is polar.


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2.
Both oxygen and sulphur are molecular. The molecules are held together by vander Waals' forces.
The larger the molecular size, the stronger the van der Waals' forces are.
Oxygen molecule is diatomic (O2), while sulphur molecule is octatomic(S8). Besides, the size of oxygen atom is smaller than that ofsulphur atom. Therefore, the size of S8 molecule is smaller than O2molecule, and thus sulphur has a higher melting point.


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3.
Dipole moment = (charge of each pole) x (distance between the twopoles)
The 1st factor is the charge of each pole. F is more electronegative than Cl,and thus F causes greater charge separation than Cl. Therefore, the charge of eachpole : C-F bond > C-Cl bond.
The 2nd factor is the distance between the two poles. Cl atom has largersize than F atom, and thus the distance between the two poles : C-Cl bond > C-F bond.
The 2nd factor outweighs the 1st factor, and thus dipole moment of C-Cl bondis greater than that of C-F bond. This leads to that CH3Cl haslarger dipole moment than CH3F.