Question

How many of the following have two $\sigma$ and two $\pi$ bonds?

$C_3^{4-},C{N}_2^{2-},C{O}_2,C_2^{2-},C_2{H}_4,C{N}^{-}$

Answer 1

$C_3^{4-}$ ion

${\left[\begin{array}{ccc}C\equiv & C-& C\end{array}\right]}^{4-}$

$\sigma$ = 2

$\pi$=2

$C{N}_2^{2-}$

${\left[\begin{array}{ccc}N=& C=& N\end{array}\right]}^{2-}$

$\sigma$ = 2

$\pi$=2

${CO}_2$

$(\stackrel{..}{\underset{..}{O}}=C=\stackrel{..}{\underset{..}{O}})$

$\sigma$ = 2

$\pi$=2

$C_2^{2-}$ :

${[C\equiv C]}^{2-}$

$\sigma$ = 1

$\pi$=2

$C_2{H}_4$

$\begin{array}{ccccc}& H& & H& \\ & |& & |& \\ H-& C& =& C& -H\end{array}$

$\sigma$ = 5

$\pi$=1

${CN}^{-}$

${[C\equiv N]}^{-}$

$\sigma$ = 1

$\pi$=2

So, only $C_3^{4-}$ , $C{N}_2^{2-}$, and ${CO}_2$ has 2$\sigma$ and 2$\pi$ bonds.