What defines the formation of an interstitial solid solution?

The formation of an interstitial solid solution is defined by the presence of smaller atoms that fit into the interstitial spaces between the larger host metal atoms in a crystalline structure. In this context, the statement that the small atom must not transfer electrons is crucial.

When smaller atoms insert themselves into the interstitial sites of a metal lattice, their electronegativity and size often lead to minimal interaction with the surrounding metal atoms. This allows them to serve primarily as fillers rather than reactants, which ensures stability in the solid solution. The small atoms typically do not form new bonds or transfer their electrons to the host lattice; they remain in a state that respects their original electronic configuration while still contributing to the alloy's overall properties.

In contrast, options emphasizing electron transfer, similar atomic radii, or the compatibility of metallic properties do not accurately capture the essence of what allows small atoms to occupy interstitial positions. While metallic properties can influence the extent of solubility, it is the lack of electron transfer during the formation of the interstitial solid solution that is particularly notable and defining.