Question

Describe, in general, the structures of ionic solids. Compareand contrast the structures of sodium chloride and zinc sulfide. How many tetrahedral holes and octahedral holes are there per closest packed anion? In zinc sulfide, why are only one-half of the tetrahedral holes filled with cations?

Short answer

The ionic solids consist of lattices of oppositely charged point charges connected in place in a balance of Columbia forces. Real ions do not occupy space; no such “perfect” ionic solid exists in nature.

Step-by-step solution

Given Data

Now, ZnS is an ionic compound that contains Zn²⁺ and S^2- ions. Zn ions are arranged in ccp. The radius ratio of ZnS is 0.40.

Zn ions are available in tetrahedral voids. Sulfide ions are found to be encircling the four Zn ions, and each Zn ion is encircled by sulfide ions tetrahedrally.

Step 2: The structures of NaCl and ZnS

NaCl structure constitutes of Na⁺ and Cl^-ions. The number of ions ${\mathbf{Na}}^{\mathbf{+}}$is equal to the number of Cl^-. The radius ratio of the NaCl is 0.524, which tells the structure has octahedral voids.

Chloride ions are available at the corners and center of each face.

Sodium ions are available in octahedral voids.

This unit cell has a face-centered arrangement, i.e., fcc.

Explanation

Tetrahedral and octahedral holes:

Two tetrahedral andone octahedral void are available per anion in a face-centered structure. The ions make the close-pack bodywork.

In hcp and ccp, one octahedral and tetrahedral voids are present.

In an interstitial site, a tetrahedral void is connected to four atoms.

Zinc sulfide:

Zn has a cubic-centered arrangement in which Zn ions are present in tetrahedral sites while sulfide ions are present at the center of the face and corners of the cube.

This means that four sulfide ions bound each Zn ion, and the sulfide ion is bounded by four Zn ions