Final answer:
The radius ratio allows us to predict the coordination number for a given ionic mineral/molecule, crucial in the structural organization of ionic compounds. It directly influences how ions pack together and the number of opposite-charged ions that surround a given ion. Option C is correct.
Step-by-step explanation:
The radius ratio allows us to predict the coordination number for a given ionic mineral/molecule. When considering the structure of ionic compounds, the radius ratio is crucial in determining how the ions pack together. The coordination number, which indicates the number of ions of opposite charge that surround a given ion, is determined by how well an ion fits within the gaps between its neighbors.
Ionic radius is used to describe the size of an ion. Taking the example of aluminum, the covalent radius of an aluminum atom is 118 pm, but when it becomes a cation like Al³⁺, the ionic radius decreases to 68 pm. The ionic sizes and their ratios to each other play a significant role in the molecular structure, as the ions arrange themselves to be in contact with as many opposite charged ions as possible.
Many cubic lattice arrangements, such as NaCl or CsCl structures, demonstrate the consequences of these ratios on the resulting ionic solid. In simpler terms, if the size of an ion within a compound is known, and if we assume the shapes and contacts of these ions, the radius ratio can help us calculate the ionic radii and predict structural properties of the compound.