Shown below is a representation of the unit cell of the mineral galena, PbS. The

Question

Shown below is a representation of the unit cell of the mineral galena, PbS. The yellow spheres represent Pb2+ ions and the gray spheres represent S2 ions. The sulfide ions occupy face-centered cubic positions in the unit cell. The lead ions occupy one octahedral hole plus several positions on the edges of the unit cell. How many formula units of lead sulfide are present in this unit cell?[1]

Shown below is a representation of the unit cell of the mineral galena, PbS. The yellow spheres represent Pb2+ ions and the gray spheres represent s ions. The sulfide ions occupy face-centered cubic positions in the unit cell. The lead ions occupy one octahedral hole plus several positions on the edges of the unit cell. How many formula units of lead sulfide are present in this unit cell? 121

Explanation / Answer

Each of the 8 corner occupied by S2- is shared with 8 cubes.

The 6 face-centered S2- are shared with 2 cubes.

Thus, the contribution of S2- to one unit cell = 8/8 + 6/2 = 1 + 3 =4

Each of the 12 edge Pb2+ is shared with 4 cubes

The center Pb2+ is not shared.

Thus, the contribution of Pb2+ to one unit cell = 12/4 + 1 = 3 + 1 =4

Total four Pb2+ ions and four S2- ions per unit cell

Therefore, galena (PbS) has 4 formula units in an unit cell.

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.