Iodine solid sublimes to Iodine gas. What happens in terms of
intermolecular forces as this process occurs?


When the Iodine solid was placed directly in a temperature equal to its
boiling point, the intermolecular forces between the Iodine molecules grew
weaker. So the Iodine particles start to move away from each other. Therefore
the Iodine solid sublimes to Iodine gas.

The Hydrogen Sulfide molecule (H2S) and the water molecule (H2O) are very similar. However, the boiling point of
Hydrogen Sulfide is -60˚C whereas the boiling point of water is 100˚C. How can
the intermolecular forces explain this difference?
 
H2O
and H2S
are both polar molecules therefore 2H2O bonded together and 2H2S bonded together have dipole-dipole force between
them. Yet the dipole-dipole force between 2H2O is a special
type of dipole-dipole force called Hydrogen bonding. Sulfur has more protons and
electrons than Oxygen so you would think that the intermolecular force of
2H2S will
be stronger than that of 2H2O and therefore the boiling point of 2H2S will be
higher. Yet 2H2O has the higher boiling point and the reason is
that 2H2O
has a hydrogen bond while H2S does not since O is one of the highest
electronegative atoms in the periodic table and it is bonded to an H atom of
another molecule in 2H2O. And since Hydrogen bond is a stronger
dipole-dipole force than that of a normal dipole-dipole bond the boiling point
of water will be greater than that of hydrogen sulfide.

Nitrogen comprises 78% of the atmosphere while oxygen comprises 21%. There two gases have low boiling points and therefore exist as gases under normal environmental conditions .How can the intermolecular forces that exist between the nitrogen molecules or oxygen molecules explain the low boiling points ?