Final answer:
The compound 12-crown-4, a smaller member of the crown ether family, is equipped to solvate smaller cations like lithium (Li+) and sodium (Na+) due to its cavity size which matches their ionic radii.
Step-by-step explanation:
Similar to 18-crown-6, the compound 12-crown-4 is part of the crown ether family, which is a class of cyclic chemical compounds that consist of a ring containing several ether groups. The number 12 in 12-crown-4 denotes the total number of atoms in the ring: 12, which includes four oxygen atoms and eight carbon atoms. The 'crown' part of the name refers to the shape of the molecule, resembling a crown, and the '4' indicates the number of ether oxygen atoms in the molecule.
The key characteristic of crown ethers is their ability to act as ligands that bind certain metal cations. Specifically, 12-crown-4 is adept at solvating metal ions that fit into the central cavity of the ether. Given its smaller ring size compared to 18-crown-6, 12-crown-4 commonly solvates smaller cations, such as lithium (Li+) and sodium (Na+), which have smaller ionic radii that are compatible with the size of the 12-crown-4 molecule.
While 18-crown-6 binds well with the larger potassium ion (K+), 12-crown-4 prefers to bind with smaller cations, showcasing how the structure of a crown ether dictates its solvation properties with various metal ions.