Question

Which one of the following molecular hybrides acts as a Lewis acid?

• A. $C{H}_4$
• B. $N{H}_3$
• C. $H_{2}O$
• D. $B{H}_3$
• E. All of these

Answer 1

The correct option is D $B{H}_3$

1. Lewis Acid: A species that accepts an electron pair (i.e., an electrophile) and will have vacant orbitals.
2. Lewis acids accept an electron pair. Lewis Acids are electrophilic meaning that they are electron attracting. When bonding with a base the acid uses its lowest unoccupied molecular orbital
3. Various species can act as Lewis acids. All cations are Lewis acids since they are able to accept electrons. (e.g., $C{u}^{2+},F{e}^{2+},F{e}^{3+}$)
4. An atom, ion, or molecule with an incomplete octet of electrons can act as an Lewis acid (e.g., $B{F}_3,Al{F}_3$).
5. Molecules where the central atom can have more than 8 valence shell electrons can be electron acceptors due to the presence of empty d-orbitals, and thus, are classified as Lewis acids (e.g., $SiB{r}_4,Si{F}_4,SnC{l}_4,S{F}_4$).
   
6. Molecules that have multiple bonds between two atoms of different electronegativities (e.g., $C{O}_2,S{O}_2$)$B{H}_3$is a lewis acid.