use the idea that intermolecular forcesare weak compared with covalent bonds to explain the bulkproperties of molecular substances.

Intermolecular forces and covalent bonds are the two main types of forces that hold molecules together. Covalent bonds are the strong forces that hold atoms together within a molecule, while intermolecular forces are the weaker forces that hold separate molecules to each other.

Because covalent bonds are much stronger than intermolecular forces, they require a lot more energy to break. This is why substances with covalent bonds often have high melting and boiling points - it takes a lot of heat energy to break these bonds and change the substance from a solid or liquid to a gas.

On the other hand, intermolecular forces are much weaker and require less energy to break. This means that substances with intermolecular forces often have low melting and boiling points because it doesn't take much heat energy to change them from a solid or liquid to a gas.

This difference in strength between covalent bonds and intermolecular forces also explains other bulk properties of molecular substances. For example, substances with covalent bonds are often hard and brittle, while substances with intermolecular forces are often soft and flexible.

Furthermore, because intermolecular forces are weaker, they allow molecules to move past each other more easily. This is why substances with intermolecular forces are often liquids or gases at room temperature, while substances with covalent bonds are often solids.

In conclusion, the weak intermolecular forces compared with the strong covalent bonds explain the bulk properties of molecular substances, including their state of matter at room temperature and their melting and boiling points.