Chapter 7.2, Problem 16LC

Interpretation Introduction

Interpretation: The arrangement of sodium ions and chloride ions in a crystal of sodium chloride needs to be described.

Concept Introduction: A matter can have mainly three states; solid, liquid, and gas. The matter is composed of atoms and in the solid state, these atoms are closely packed giving the solid a rigid shape.

Solids can be crystalline or amorphous. In crystalline form, the atoms, molecules, and ions are in a symmetrical form. On the other hand, amorphous solids are not symmetrical. A crystal lattice is formed by unit cells that combine to form a network. Also, the two types of packing in solids are cubic close packing and hexagonal close packing.

Explanation of Solution

In NaCl crystal, chloride ions are arranged in ccp type. Here, chloride ions are at the corners as well as center of each face of the cube. One sodium ion has 6 chloride ions surrounding it. Thus, sodium ions occupy all octahedral sites. For every chloride ion, there is only one octahedral site. Here, each chloride ion is also surrounded by 6 sodium ions. Thus, cations and anions are present in equivalent positions. The coordination number of both sodium and chlorine is 6.

The arrangement can be represented as follows: