Chapter 8.2, Problem 13LC

Interpretation Introduction

Interpretation: The three ways need to be listed by which the octet rule can sometimes fail to be obeyed.

Concept Introduction: According to the octet rule, atoms of an element can gain, lose or share electrons to achieve noble gas electronic configuration.

Explanation of Solution

In some cases, molecules can have an odd number of electrons, molecules can have atoms with more or less than 8 electrons. Thus, three ways in which the octet rule can sometimes fail to be obeyed are as follows:

Molecules with an odd number of electrons:

NO molecule has an odd number of electrons. The molecule is stable but the octet is not complete. Here, the number of valence electrons in N and O atoms is 5 and 6 respectively thus, the total number of valence electrons is 11. Since there is an odd number of electrons in the molecule, each atom cannot have an octet of electrons.

Molecules with more than 8 electrons:

When there is more than an octet of electrons in a molecule, it is said to be an expanded-valence molecule. For example, in ${\text{SF}}_{\text{6}}$ molecule, a sulfur atom has more than 8 electrons; thus, the octet rule is not obeyed.

Molecules with less than 8 electrons:

In ${\text{BCl}}_{\text{3}}$ molecule, the boron atom has less than 8 electrons; thus, the octet rule is not obeyed. Here, boron has 6 valence electrons and each carbon atom has 8 electrons. The octet for chlorine is achieved. The lone pair of electrons from one of the chlorine atom form a B-Cl double bond.