* Ionic Radius: Fluoride ions (F⁻) are much smaller than chloride ions (Cl⁻). This difference in ionic radius significantly influences the packing arrangement of the ions in the crystal lattice.
* Coordination Number: The smaller size of fluoride ions allows calcium to coordinate with a higher number of fluoride ions. This results in a different crystal structure.
* Structure:
* Calcium fluoride (CaF₂): Has a fluorite structure, where each calcium ion is surrounded by 8 fluoride ions, and each fluoride ion is surrounded by 4 calcium ions.
* Calcium chloride (CaCl₂): Has a rutile structure, where each calcium ion is surrounded by 6 chloride ions, and each chloride ion is surrounded by 3 calcium ions.
In summary: The difference in ionic radii between fluoride and chloride ions leads to different coordination numbers and ultimately, different crystal structures for calcium fluoride and calcium chloride.
