Chemical Bonding And Molecular Structure Ques 123

Solution:

123. (b) $CN^{-}$and $CO$ have same no. of electrons and have same bond order equal to 3 .

Short cut trick to calculate the bond order:

$N_2$ has 14 electrons and its bond order is 3 . We have to remember this concept that every electron added or subtracted to 14 , reduces the bond order by 0.5 . For example

$CN^{-} \Rightarrow$ no. of electrons $=6+7+1=14$

$\therefore$ bond order $=3$

$CO \Rightarrow$ no. of electrons $=6+8=14$

$\therefore$ bond order $=3$

NO $\Rightarrow$ no. of electrons $=7+8=15$

$\therefore$ bond order $=3-0.5=2.5$

$NO^{+} \Rightarrow$ no. of electrons $=7+8-1=14$

$\therefore$ bond order $=3$

$O_2{ }^{-} \Rightarrow$ no. of electrons $=8+8+1=17$

$\therefore$ bond order $=3-1.5$

Please note that this method will work for any species that have electrons between 10 and 18 .