Lithium fluroide `(LiF)` is mainly ionic but lithium iodide `(LiI)` is covalent in nature. Assign reason.

Explanation

`I^(-)` ion has a bigger size than the `F^(-)` ion. It can be more readily polarised by `Li^(+)` ion than by `F^(-)` ion. As a result, `Li^(+) " and " I^(-)` ions come quite close and neutralise their charge to a large extent resulting in covalent compound. On the other hand, `Li^(+) " and " F^(-)` ions are not in a position to neutralise their charge and `LiF` is mainly ionic.