Boron forms [BF4]- while aluminium forms [AlF6]3- Why - Chemistry - Classification of Elements and Periodicity in Properties

Question

Boron forms [BF4]- while aluminium forms
[AlF6]3- Why?

Pushkar Shukla · Accepted Answer

Boron has Electronic configuration as:
[He]2s22p1 and Aluminum as :
[Ne]3s23p1
However Al has vacant 'd' orbitals and can expand its octet in
[AlF6]- whereas, boron cannot expand its
octet and hence gets restricted upto
[BF4]-

Boron forms [BF4]- while aluminium forms [AlF6]3-. Why?

Boron forms [BF₄]^-while aluminium forms [AlF₆]^3-. Why?