You would expect strontium to be chemically more similar to calcium because they are in the same group/family on the periodic table. The elements in the same group generally have similar chemical properties because they have the same number of valence electrons. In this case, both calcium and strontium belong to group 2, also known as the alkaline earth metals. These elements share a similar electron configuration in their outermost energy level, specifically 2 valence electrons. As a result, they tend to exhibit similar chemical behavior and form similar compounds.
