Chapter 7, Problem 87A

Interpretation Introduction

Interpretation : The chemically similar alkali metal chlorides NaCl and CsCl have different crystal structures whereas the chemically different NaCl and MnS have the same crystal structures is to be inferred.

Concept Introduction : Cations and anions combine to form an ionic compound.

The cation of metal and anion of non-metal are the main components of ionic compounds.

Answer to Problem 87A

NaCl and CsCl have different crystals due to different coordination numbers.

NaCl and MnS have the same crystal structure due to the same coordination number.

Explanation of Solution

Even though ionic compounds are formed of ions, they have no electrical charge. The total negative charge of an anion is equal to the sum of the positive charges of cations.

The coordination numbers of NaCl and CsCl are different whereas the coordination number of NaCl and MnS are the same.

The quantity of ions with opposing charges that surround an ion in a crystal is known as its coordination number.

  ${\text{Na}}^{+}$ has a coordination number of 6. Each ${\text{Na}}^{+}$ ion is surrounded by six ${\text{Cl}}^{-}$ ions.

Each ${\text{Cl}}^{-}$ ion has a coordination number of 6 and is surrounded by 6 ${\text{Na}}^{+}$ ions.

CsCl has a different crystal structure due to its larger size.

But in CsCl structure, each ${\text{Cs}}^{+}$ ion is surrounded by eight ${\text{Cl}}^{-}$ ions and each ${\text{Cl}}^{-}$ is surrounded by eight ${\text{Cs}}^{+}$ ions.

MnS and NaCl have similar sizes so they have the same coordination number.