Sodium hydride, NaH, crystallizes in a face-centered cubic unit cell similar to that of NaCl (Figure 12.11). How many Na+ ions touch each H- ion, and how many H- ions touch each Na+ ion?

Verified step by step guidance

1. Identify the structure of the face-centered cubic (fcc) unit cell, which is characterized by atoms at each of the eight corners and one atom at the center of each face of the cube.
2. Recognize that in a NaCl-type structure, the cations (Na+) and anions (H-) alternate positions in the lattice. Each type of ion is surrounded by the other type in the structure.
3. Determine the coordination number for each ion, which is the number of nearest neighboring ions of the opposite charge that an ion touches directly. In an fcc lattice like NaCl, each ion is surrounded by six ions of the opposite charge.
4. Apply this understanding to NaH, where Na+ ions and H- ions alternate in the same manner. Each Na+ ion is surrounded by six H- ions and vice versa.
5. Conclude that in the NaH structure, each Na+ ion touches six H- ions, and each H- ion touches six Na+ ions.

Key Concepts

Ionic Bonding

Ionic bonding occurs when atoms transfer electrons, resulting in the formation of charged ions. In sodium hydride (NaH), sodium (Na) donates an electron to hydrogen (H), creating Na+ and H- ions. Understanding ionic bonding is crucial for analyzing the interactions between these ions in the crystal lattice.

Crystal Lattice Structure

A crystal lattice structure is a three-dimensional arrangement of atoms or ions in a crystalline material. In the case of NaH, it adopts a face-centered cubic (FCC) structure similar to NaCl, where each ion occupies specific positions in the lattice. This arrangement influences how ions interact with each other, including how many of one type of ion are in contact with another.

Coordination Number

The coordination number refers to the number of nearest neighbor ions surrounding a given ion in a crystal lattice. For NaH, determining how many Na+ ions touch each H- ion and vice versa involves calculating the coordination numbers for both ions based on their positions in the FCC structure. This concept is essential for understanding the spatial relationships and interactions between ions in the lattice.