Chapter 9, Problem 12Q

Interpretation Introduction

Interpretation:

The reason for chalk having higher melting point than motor oil and water has to be justified.

Concept introduction:

• Matter exists in three distinct physical forms – solid, liquid and gas. There are two types of interactions present in matter – intramolecular meaning, “within the molecule” and intermolecular meaning “between the molecules”.

• Intramolecular force refers to the type of bonding that holds the atoms or ions together to form a stable molecule. Intermolecular force refers to the type of interaction that exists between the so formed molecules by bonding. 

• The physical properties of a substance such as boiling point, melting point, vapor pressure, etc., of a substance depend on the type and strength of the intermolecular force exists in it. Higher the strength of these forces, higher will be the melting and boiling point. The classification is summarized as follows –

               

                                                               Figure 1

                Intramolecular forces are nothing but the type of bonding between them. Ionic compounds have electrostatic force of attraction, called “ionic bond” the strongest one. Atoms having high electronegativity difference with each other forms ionic bond. An atom having slight electronegativity difference with other atom forms covalent bonds. They are of two types, that is polar and non-polar depend upon the polarity of the atoms. Metallic bond is formed between the metal atoms.

        

                                                               Figure 2

                Intermolecular forces are Van der Waals forces. They are weak and are of categories - London dispersion forces, dipole-dipole forces and hydrogen bonding. Hydrogen bonding is relatively the strongest one. It is formed in polar covalent compounds containing hydrogen and other high electronegativity like fluorine, oxygen or nitrogen. These atoms in a molecule partially bond to hydrogen of the other same molecule or within a molecule.