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-Nitrogen comprises 78% of the atmosphere while Oxygen comprises 21%. These two gases have low boiling points and therefore can exist as gases under normal environmental conditions. How can the inter molecular forces that exist between Nitrogen molecules or Oxygen molecules explain the low boiling points?
As previously mentioned, non-polar molecules apply London dispersion forces. So these forces occur in Nitrogen and Oxygen molecules and since they are very weak, they require very low amounts of energy to be broken. Therefore we conclude that these Nitrogen and Oxygen boil at low temperatures because the inter molecular forces occurring within each gas lack strength.
-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 inter molecular forces explain this difference?
Both hydrogen sulfide and water molecules are polar having a total net dipole. They also share the same geometric structure. However this is not the issue here. Oxygen (O) in water is more electronegative than Sulfur (S) in hydrogen sulfide. Since they both have a net dipole, then the attraction between hydrogen and Oxygen is greater than between hydrogen and Sulfur. This is why we say that water has a hydrogen bond (hydrogen covalently bonded with either O, N, or F), while hydrogen sulfide has dipole-dipole forces. Hydrogen bonds are said to be the strongest between all inter molecular forces because hydrogen would be bonded to highly electronegative atoms that increase the polarity and the forces so they will require more energy and greater temperatures to be broken. This explains the high boiling point of water in comparison with hydrogen sulfide.
Iodine solid sublimes to iodine gas. What happens in terms of inter molecular forces as this process occurs?
The inter molecular forces are being broken because they are the forces that keep a compound altogether and after they break the molecules drift away from each other until they constitute the properties of a gas, where the particles are really far away from each other.