What type of molecules typically have low melting and boiling points?

Covalent compounds typically have low melting and boiling points due to the nature of the forces holding their molecules together. In covalent compounds, non-metal elements share electrons to form molecules. These molecules are held together by relatively weak intermolecular forces, such as van der Waals forces or dipole-dipole interactions, rather than the stronger ionic bonds found in ionic compounds or metallic bonds in metallic substances.

Because these intermolecular forces are weaker, less energy is required to overcome them when changing states from solid to liquid or from liquid to gas. As a result, many covalent compounds exist as gases or liquids at room temperature, and they demonstrate lower melting and boiling points compared to ionic or metallic compounds, which have much stronger attractions between their particles.

In contrast, ionic compounds typically have high melting and boiling points due to the strong electrostatic forces between positively and negatively charged ions. Metallic compounds, with their delocalized electrons, also have properties that confer higher melting and boiling points. Alloys, which are mixtures of metals, can exhibit a range of properties depending on their composition but generally will not have the characteristics associated with low melting and boiling points as seen in covalent compounds.