Question

Which of the following are Lewis acids?
This question has multiple correct options
A) $P{H_3}$ and $SiC{l_4}$
B) $BC{l_3}$ and $AlC{l_3}$
C) $P{H_3}$ and $BC{l_3}$
D) $AlC{l_3}$ and $SiC{l_4}$

Answer 1

Hint: According to the theory of Lewis of Acids and Bases a Lewis Acid is an atom or compound which accepts an electron pair. In the question, the Lewis acidity of the structure has been asked and one needs to analyze which structures can act as Lewis acid by seeing its incomplete octet.

Complete step by step answer:
Complete step by step answer:
1) First of all we will learn about the concept of Lewis acid where they are the chemical species that are able to accept electron pairs and have empty orbitals. Due to the presence of empty orbitals the structure needs to accept the electron pairs to complete its octet and get itself stabilized.
2) Now let's analyze the given structure which can act as Lewis acids. The structures $P{H_3}$ and $SiC{l_4}$ the $P{H_3}$ has lone pair of electrons hence it is a Lewis base and $SiC{l_4}$ has a vacant orbital and acts as a Lewis acid. As one structure is Lewis base this option is incorrect.
3) The structure $BC{l_3}$ and $AlC{l_3}$ have both vacant p-orbital and incomplete octet hence this option is correct.
4) The structure $P{H_3}$ and $BC{l_3}$ as we have seen above the $P{H_3}$ acts as Lewis base hence this option is incorrect.
5) The structures $AlC{l_3}$ and $SiC{l_4}$ both have vacant orbital and incomplete octet hence this option is correct.
6) Therefore, after analyzing all the structure $BC{l_3}$ , $AlC{l_3}$ and $AlC{l_3}$ , $SiC{l_4}$ are Lewis structures

So, the correct answer is Option B,D .

Note:
In most of the reactions Lewis acids act as an activating agent as they are accepter of lone pair of electrons. The benzene ring which is electron-rich can be activated by using Lewis acid such as $AlC{l_3}$. An incomplete octet is determined by an element’s vacant positions present in it and one can find out by writing the electronic configuration for that element. The elements with vacant p and d orbital gives the Lewis acid structure.