Final answer:
The 18-crown-6 ether, a crown ether with an 18-membered ring and six oxygen atoms, can solvate sodium ions in aqueous solutions through ion-dipole interactions, despite being ideally sized for potassium ions.
Step-by-step explanation:
The molecule 18-crown-6 is a type of crown ether that is well-known for its ability to solvate positively charged metal ions through its cavity which is lined by oxygen atoms. Crown ethers are considered cyclic polyethers that contain several ether groups in a ring structure. The '18' in 18-crown-6 indicates that it is an 18-membered ring with six oxygen atoms, which are spaced out by two or three carbon atoms, capable of coordinating to the metal ion. Each of the oxygen atoms can effectively donate a pair of electrons to a positive ion like sodium to form a stable coordination complex, thus solvating it.
Despite 18-crown-6 being a great fit for a potassium ion (K+), it can still accommodate a sodium ion (Na+), although the fit may not be as perfect due to the size difference between the two ions. In contrast, its ability to solvate is based on the principle of ion-dipole interaction, where the dipole moment of the ether oxygen atoms can stabilize the positive charge of the metal ion. The cavity of the 18-crown-6 ether provides a microenvironment that enhances the solvation of ions like sodium when in aqueous solution.