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Why is AlF3 not hypovalent?

Answer
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Hint: Hypervalent compounds are those in which the central main group element contains less than eight electrons. AlF3 is an ionic compound because of the large electronegativity of fluorine. In +3 oxidation state. Aluminium has electronic configuration 1s22s22p6.

Complete answer:
Aluminium belongs to group number 13 and period number 3. It is a p-block element with electronic configuration [Ne]3s23p1. 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 1s22s22p6 i.e. complete octet. Therefore, the central main group element has eight valence electrons. Therefore, AlF3 is not hypovalent.

Additional information:
Besides AlF3, AlCl3 and AlBr3 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, PCl5. Generally, Hypervalent compounds are lewis acids as they have the capability to accept a pair of electrons to complete its octet. For examples, AlCl3 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 AlF3 an ionic compound. Thus, the electronic configuration of aluminium in +3 oxidation state is 1s22s22p6. Therefore, the central main group element has eight valence electrons which makesAlF3 not hypovalent.