Question

Which of the molecules is not hypervalent but complete is octet?
a.) $AlC{l_3}$
b.) $AlB{r_3}$
c.) $Al{F_3}$
d.) $B{F_3}$

Answer 1

Hint: Before attempting this question one should have prior knowledge about the concept of hypervalent according to which electrons with less than 8 valence electrons are said to be hypervalent, use this information to approach towards the solution to the question.

Complete step by step solution: The compounds are said to be hypervalent if the central atom has less than “eight valence electrons'” Hypervalent compounds have negative charge due to the affinity towards electrons.
An octet is complete when an electron has 8 valence electrons which means it is stable. According to the question, the options are given as$AlC{l_3}$,$AlB{r_3}$, $Al{F_3}$ and $B{F_3}$
So, as we known $AlC{l_3}$ is covalent in nature which means, it has less than 8 valence electrons, thereby $AlC{l_3}$ is hypervalent
Similarly, $AlC{l_3}$ has configuration $4{s^2}4{p^5}$ which means it has 7 valence electrons, and it is also a hypervalent compound but $Al{F_3}$ is not a hypervalent compound because it’s an ionic compound because Al has +3 valence electrons which are shared with electrons of 3 F atoms
Now, the total valence is 6 electrons.
Hence, 1 F atom donates one lone pair of electrons, which means 2 electrons. Thus, completing the octet of Al. Therefore, it has 8 electrons in its outermost valence shell which means $Al{F_3}$ is not hypervalent and it also completes the octet.

Hence, option C is the correct option.

Note: In the above solution we used a term “valence electron” which can be explained as the electrons which are present in the outer shell of an electrons, when an atom participate in the chemical bond valence electrons take part in forming bonds which depend upon the vacancy of electron in other atom the bonds form by the valence electrons are single covalent bond, double covalent bond by sharing 1 or 2 valance electrons with other atom.