Question

In which pair of species, the octet rule is not obeyed?

• A. ${PF}_5$ and $PO{Cl}_3$
• B. ${BCl}_3$ and ${PCl}_5$
• C. ${CF}_4$ and ${NF}_3$
• D. ${NH}_3$ and $N{Cl}_3$

Answer 1

The correct option is B ${BCl}_3$ and ${PCl}_5$

1. To find the species which does not obey the octet rule is calculated by calculating the total number of electrons in the species.

2. Total number of electrons is calculated by the number of bonded electrons + number of electrons in lone pairs

3. $PC{l}_5$ = Five bond pairs, no lone pair. It means it has total of 10 electrons

$BC{l}_3$ = three bond pairs, no lone pair. So it has total 6 electrons.

4. Species having electrons less than 8 or more than 8 will not obey the octet rule.