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In this section, some students have sent us questions on intermolecular forces, and we have joyfully answered them. Leave a comment if you have any questions or would like to say something.

Questions

Question 1: Nitrgen compromises 78% of the atmosphere while oxygen compromises 21%. These two gases have low boiling points and therefore can exist as gases under normal environmental conditions. How can the intermolecular forces that exist between the nitrogen molecules or the oxygen molecules explain the low boiling points? (Asked by Paolo from Spain)

Question 2: The hydrogen sulfide molecule (H2S) and the water molecule (H2O) are very similar. However, the boiling point of hydrogen sulfide is -60 degrees Celsius whereas the boiling point of water is 100 degrees Celsius. How can the intermolecular forces explain this difference? (Asked by Biggie from West Coast)

Question 3: Iodine solid sublimes to iodine gas. What happens in terms of intermolecular forces as this process occurs? (Asked by Chantal from Mansourieh)

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Answers

Answer 1: In molecules, the stronger the intermolecular forces, the higher the boiling points. In this case, the intermolecular forces must be weak, or in other words the atoms are far apart. This will result in a low boiling point since not a lot of energy is required to break the bonds. That is why nitrogen and oxygen can exist as gases under normal environmental conditions.

Answer 2: As previously said, the stronger the intermolecular forces, the higher the boiling point. So as a result, the weaker the intermolecular forces, the lower the boiling point. H2O and H2S are similar molecules. They have the same molecular geometry and are both polar. But since the oxygen atom in water is much more electronegative than the sulfur atom in hydrogen sulfide, it will result in a much more polar bond. In other words, the H2O molecule has much stronger bonds than the H2S molecule. Since the bonds of H2O are stronger, the intermolecular force is also greater, so the boiling point of the molecule is high. And since the bonds of H2S are weak, the intermolecular force is also weak, resulting in the boiling point to be much lower.

Answer 3: Sublimation occurs when a molecule changes from its solid state to its gaseous state without going through the liquid state. As the iodine solid sublimes to gas, its intermolecular forces weaken throughout the process. When it first starts, its intermolecular forces are strong, and as it reaches to its gas state, the intermolecular forces diminish, resulting with no intermolecular forces.