Question

How many of the following species contain only sigma (2c-2e) bonds?

$BO_3^{-}$, trimer of $HBO_2$, $SiO_4^{-}$, $O_2^{-}$, $O_2$, $SiO_2$(solid), $C_3O_2$, $SO_4^{2-}$, $CO_3^{2-}$, $NO_3^{-}$, $H_2O_2$, $S_2^{2-}$

• A. 2
• B. 3
• C. 4
• D. 5

Answer 1

Answer: (C)

4 species.

Answer 2

The species that have only two‐center two‐electron sigma bonds are:

• SiO₄⁻
• SiO₂ (solid)
• H₂O₂
• S₂²⁻

$BO_3^{-}$, trimer of $HBO_2$, $O_2^{-}$, $O_2$, $C_3O_2$, $SO_4^{2-}$, $CO_3^{2-}$, $NO_3^{-}$ contain π–bonds (or delocalized π systems).