Question

Why does SiF4 act as a lewis acid?

Answer 1

`"SiF"_4` can act as a Lewis acid because `"Si"` can expand its octet.

Explanation:

A Lewis acid is an electron-pair acceptor.

(from chemwiki.ucdavis.edu)

`"SiF"_4` can accept electron pairs and expand its octet to 12.

For example, it reacts with `"F"^-` to form `"SiF"_6^(2-)` [hexafluoridosilicate(2-)]