NaCl crystallizes in a face- centered cubic cell. What is the total number of ions (Na⁺ions and Cl^- ions) that lie within a unit cell of NaCl? A) 6 B) 2 C) 4 D) 8 E) 5

Question

Quizplus · Accepted Answer

In NaCl, each Na+ ion is surrounded by six chloride ions and each Cl- ion is surrounded by six sodium ions. Therefore, there are 4 ions within a single unit cell: 1 Na+ ion and 1 Cl- ion at the corners of the cell (each contributing 1/8th of an ion to the cell) and 2 Na+ ions and 2 Cl- ions on the faces of the cell (each contributing 1/2 of an ion to the cell). Thus, the total number of ions in a unit cell of NaCl is:

1 Na+ ion x 1/8 + 1 Cl- ion x 1/8 + 2 Na+ ions x 1/2 + 2 Cl- ions x 1/2 = 1 + 1 + 1 + 1 + 2 + 2 = 8

Therefore, the correct answer is (D) 8.

NaCl Crystallizes in a Face- Centered Cubic Cell