Understanding Coordination Number

The coordination number of an ion in a crystal lattice refers to the number of oppositely charged ions that directly surround it.

Structure of BaCl₂

* Crystal Structure: BaCl₂ crystallizes in a face-centered cubic (FCC) lattice.

* Arrangement: Barium (Ba²⁺) ions occupy the corners and face centers of the cubic unit cell, while chloride (Cl⁻) ions occupy the edges and the center of the unit cell.

Coordination Number Calculation

* Barium (Ba²⁺): Each Ba²⁺ ion is surrounded by 8 Cl⁻ ions (6 from the face centers and 2 from the edges). Therefore, the coordination number of Ba²⁺ is 8.

* Chloride (Cl⁻): Each Cl⁻ ion is surrounded by 6 Ba²⁺ ions (2 from the corners and 4 from the face centers). Therefore, the coordination number of Cl⁻ is 6.

Summary

In BaCl₂, the coordination number of:

* Ba²⁺ is 8

* Cl⁻ is 6