On the basis of ionic charge and ionic radii given in Table...

On the basis of ionic charge and ionic radii given in Table $12.3,$ predict crystal structures for the following materials: (a) $\mathrm{CaO},$ (b) $\mathrm{MnS}$
(c) $\mathrm{KBr},$ and
(d) $\mathrm{CsBr}$. Justify your selections.

Key Concepts

Ionic Charge

Ionic charge refers to the positive or negative electrical charge carried by an ion. In crystal structures, these charges determine the strength of electrostatic attractions between ions, which influences the overall stability of the material and can affect the preferred arrangement of ions in the lattice.

Ionic Radii

Ionic radii denote the effective size of an ion, which plays a crucial role in the spatial arrangement of ions in a crystal lattice. The relative sizes of the cations and anions determine how closely the ions can pack together, influencing the coordination environment and the overall geometry of the structure.

Radius Ratio Rule

The radius ratio rule is a guideline used to predict the coordination number and, consequently, the crystal structure of an ionic compound based on the ratio of the cation radius to the anion radius. This rule helps determine which coordination geometries are geometrically feasible, thereby aiding in the prediction of structural types such as octahedral or cubic arrangements.

Coordination Number

Coordination number is the number of oppositely charged ions that surround a given ion in a crystal lattice. It is directly influenced by the ionic radii and the radius ratio, and it plays a key role in determining the most stable packing geometry in ionic solids.

Crystal Structure Prediction

Crystal structure prediction involves using factors such as ionic charge, ionic radii, the radius ratio rule, and coordination number to determine the most likely arrangement of ions in an ionic compound. This prediction helps in identifying whether a material will adopt structures like the NaCl type (octahedral coordination) or the CsCl type (cubic coordination), among other possible geometries.

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