Covalent molecules have low melting and boiling points because of their weak intermolecular forces.The force of attraction between the molecules in a covalent compound is weak, so it takes little energy to break the bonds.

Yes, all covalent compounds have a three-dimensional structure due to the directional nature of covalent bonds, which means the atoms within a molecule are arranged in a specific spatial orientation, giving the molecule a definite shape in three dimensions; this is explained by the Valence Shell Electron Pair Repulsion (VSEPR) theory.