Question

Why is $Al{{F}_{3}}$ not hypovalent?

Answer 1

Hypervalent compounds are those in which the central main group element contains less than eight electrons. $Al{{F}_{3}}$ is an ionic compound because of the large electronegativity of fluorine. In $+3$ oxidation state. Aluminium has electronic configuration $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}$.

Complete answer:
Aluminium belongs to group number $13$ and period number $3$. It is a p-block element with electronic configuration $[Ne]3{{s}^{2}}3{{p}^{1}}$. Since fluorine is the most electronegative element of the periodic table. Thus, when it is bonded to aluminium it will accept electrons from aluminium easily. Therefore, an ionic bond is formed between aluminium and fluorine. After donation of electrons, aluminium exists in $+3$ oxidation state. In $+3$ oxidation state, aluminium has electronic configuration $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}$ i.e. complete octet. Therefore, the central main group element has eight valence electrons. Therefore, $Al{{F}_{3}}$ is not hypovalent.

Additional information:
Besides $Al{{F}_{3}}$, $AlC{{l}_{3}}$ and $AlB{{r}_{3}}$ are also exist. In latter compounds, covalent bond is formed between central main group element and chlorine/bromine. Therefore, in these cases, the central main group element has six valence electrons and is thus hypervalent in nature. Apart from hypervalent compounds, hypervalent compounds also exist in which the central main group element has more than eight electrons. For instance, $PC{{l}_{5}}$. Generally, Hypervalent compounds are lewis acids as they have the capability to accept a pair of electrons to complete its octet. For examples, $AlC{{l}_{3}}$ is a well-known lewis acid catalyst used in the electrophilic substitution of benzene such as Friedal’s craft alkylation and acylation.

Note:
It is important to note that greater electronegativity of fluorine makes $Al{{F}_{3}}$ an ionic compound. Thus, the electronic configuration of aluminium in $+3$ oxidation state is $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}$. Therefore, the central main group element has eight valence electrons which makes$Al{{F}_{3}}$ not hypovalent.