Chapter 14, Problem 36A

Interpretation Introduction

Interpretation:

The difference in physical properties between ionic solids and molecular solids have to be described. The fundamental particles in each solid have to be explained. To illustrate this, the examples have to be given.

Concept Introduction:

Crystalline solids are solid compounds with highly ordered structure of the constituents (atoms, molecules or ions). Depending on the constituents (atoms, molecules or ions), the crystalline solids are classified in three types-

1. Ionic solids
2. Molecular solids
3. Atomic solids

Explanation of Solution

The physical properties of crystalline solids-

1. Hardness
2. Melting point
3. Boiling point
4. conductance

The ionic solids are hard, they have high melting points and high boiling points. As ionic solids contain ions, aqueous solution of ionic solid conducts electricity.

The difference in these properties can be explained by considering intermolecular attractive forces which hold the constituents together inside the solids. Intermolecular attractive force in ionic solids is the electrostatic attraction between two oppositely charged ions which is very strong. Due to this attraction, the ions are held together very tightly. Thus, the ionic solid is very hard. As it is very difficult to separate the ions, melting points and boiling points become high for ionic compounds. Whereas molecular solids consist of molecules. The molecules in a molecular solid are held together by weak Van der Waals forces.

NaCl is an ionic solid which contains Na+ and Cl- ions. NaCl has high melting point and high boiling point. The aqueous solution of NaCl conducts electricity because of Na+ and Cl- ions.

S₈ is a molecular solid. S₈ is a soft solid and it has lower melting point and lower boiling point. It does not conduct electricity.