This is a general question, not specific to any one homework problem just a concept I must understand in order to figure out all of my homework. Does clustering tendency increase as atomic radii between substances A and B become more similar? Clustering tendency may not be particularly clear. What I mean is if there is a substance A and B with very similar atomic radii, are they more likely to dislike eachother or like eachother. Lets say A is MgO and B is NiO. This now is a specific homework question, admittedly. It seems to me that A and B would like eachother becuase the radius of Mg = radius Ni and therefore there would be a low clustering tendecny - that is MgO would not feel compelled to stay with other MgOs becuase NiO is a comparable substance. However MgO and CaO would want to self-cluster because they dislike each other because the radi between Mg and Ca is drastically different. Is this logic incorrect?