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Chapter 12: 12.91P (page 497)

Calcium sulfide adopts the sodium chloride crystal structure (Figure). How manyS2-ions are in the CaS unit cell?

Short Answer

Expert verified

FourS2- ions are present in the CaS unit cell

Step by step solution

01

Sodium chloride structure

Sodium chloride structure is an anion-occupied face-centered array with cations occupying interpenetrating FCC lattice.

02

Ions in the unit cell

The face-centered cubic unit cell consists of 8 anions in the corner, thus one anion contributing18 to the unit cell. Along with that, anions are present in the center of the six respective faces of the cell. Hereby, each anion contributing12 to the unit cell.

Thus, each unit cell consists of 8×(18)+6×(12)=4, i.e., four anions in the unit cell.

Similarly, for cations, the ions are arranged in an FCC array, thus four cations in the unit cell.

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