Chapter 2, Problem 1CTQ

Interpretation Introduction

Interpretation : Whether each molecule or ion in figures 2.2 and 2.3 are legitimate Lewis structures or not should be confirmed.

Concept Introduction : A legitimate Lewis structure is an electron dot and line bond representation in which the total number of valence electrons is indicated. Number of valence electrons around hydrogen is two. Number of valence electrons around carbon, nitrogen, oxygen, fluorine atom is eight. This is called the octet rule.

Answer to Problem 1CTQ

All the given Lewis structures are legitimate.

Explanation of Solution

In ${\text{H}}_2\text{O}$ ,

Total number of valence electrons = $\left(1\times 2\right)+6=8$

Number of electrons consumed for bonds = $\left(2\times 2\right)=4$

Number of remaining electrons = $8-4=4$

The remaining four electrons are added to oxygen atom. Then it completes its octet. Therefore, given Lewis structure for water molecule is a legitimate structure.

In ${\text{F}}_2$ ,

Total number of valence electrons = $\left(7\times 2\right)=14$

Number of electrons consumed for bonds = $\left(1\times 2\right)=2$

Number of remaining electrons = $14-2=12$

The remaining twelve electrons are added to two fluorine atom six for each. Then those complete their octet. Therefore, given Lewis structure for ${\text{F}}_2$ molecule is a legitimate structure.

In ${\text{O}}^{2-}$ ,

Total number of valence electrons = $6$

Number of electrons gained from negative charges = $2$

Total Number of electrons = $6+2=8$

Therefore, given Lewis structure for ${\text{O}}^{2-}$ molecule is a legitimate structure.

In ${\text{NH}}_3$ ,

Total number of valence electrons = $5+\left(1\times 3\right)=8$

Number of electrons consumed for bonds = $\left(2\times 3\right)=6$

Number of remaining electrons = $8-6=2$

The remaining two electrons are added to nitrogen atom. Then it completed its octet. Therefore, given Lewis structure for ${\text{NH}}_3$ molecule is a legitimate structure.

In $\text{HF}$ ,

Total number of valence electrons = $1+7=8$

Number of electrons consumed for bonds = $\left(2\times 1\right)=2$

Number of remaining electrons = $8-2=6$

The remaining six electrons are added to fluorine atom. Then it completed its octet. Therefore, given Lewis structure for $\text{HF}$ molecule is a legitimate structure.

Conclusion

Thus, all the given Lewis structures are legitimate.