Chapter 6, Problem 6.1KSP

Which of the following atoms must always obey the octet rule? (Select all that apply.)

(a) C

(b) N

(c) S

(d) Br

(e) Xe

Interpretation Introduction

Interpretation:

The elements that always obey octet rule should be identified from the given options.

Concept Introduction:

• Lewis structures are diagrams that represent the chemical bonding of covalently bonded molecules and coordination compounds.
• It is also known as Lewis dot structures which represents the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.
• The Lewis structure is based on the concept of the octet rule so that the electrons shared in each atom should have 8 electrons in its outer shell.
• Atoms can be stable even though the number of valence electrons in the atoms in a molecule is less than 8 and is called incomplete octet
• Atoms can be stable even though the number of valence electrons in the atoms in a molecule is more than 8 and is called expanded octet

To determine: elements that always obey octet rule.

Answer to Problem 6.1KSP

(a) $\text{C}$

(b) $\text{N}$

Explanation of Solution

Reason for correct option

$\text{C}\text{and}\text{N}$ are elements in group 4A and 5A respectively.  These elements always tend to have octet electrons around them.  Since these three elements are in the second period row the elements, bonds are formed due to the presence of vacant orbital in the $\text{2s 2p}$ orbitals.  There are no further vacant orbital to form an expanded octet by easily accept additional electrons

The elements that cannot have more than an octet electron are $\text{C}\text{and}\text{N}$

Hence the elements that cannot have more than an octet electron are option a, and b

Reasons for incorrect options:

Write all the elements that cannot have more than an octet electron in the options except option a, and b.

(c) $\text{S}$

(d) $\text{Br}$

(e) $\text{Xe}$

The elements that always obey octet rule are $\text{C}\text{and}\text{N}$

In $\text{S, Br and Xe}$ due to the presence of empty d orbital, they can easily accept additional electrons and hence violates octet rule.  They have an expanded octet.

So, the elementsthat always obey octet rule are not matching with any of the above the elementsthat always obey octet rule in remaining options.

Hence the incorrect options are c, d and e.

Conclusion

The correct options for the elements that always obey octet rule are identified from the given options.