Question

Lithium chloride crystallizes in a face-centered cubic unit cell with chloride ions occupying the lattice points and lithium ions occupying octahedral holes. How many chloride ions surround each lithium ion in LiCl? Hint: make a sketch of a lithium ion in an octahedral hole in LiCl(s).

Answer 1

Answer:

6 chloride ions surround each lithium ion in LiCl unit cell.

Explanation:

Lithium chloride crystallizes into face-centered cubic unit cell.

Face-centered cubic structures are type of cubic close packing.

Number of octahedral voids in ccp = n

Number of tetrahedral voids in ccp = 2n

n = number of atoms or ions in the packing

In FCC , crystal lattice there are 4 atoms.

Number of octahedral voids in FCC= 4

1 octahdreal void is present at center of the cube and 12 octahedral voids are present at the center of 12 edges of the cube. Each edge of a cube is shared by 4 unit cells.

1+ $\frac{12}{4}$ = 4

In unit cell of LiCl, lithium is present at octahedral void. And each octahedral void is surrounded by 6 chlorine atoms.

As chlorine ions present at all the faces of the cube are touching lithium ion present in an octahedral void.