Whether Vs If

1). After Prepositions , we use only whether.

I haven't settled the question of whether I'll go back home.
There was a big argument about whether we should move to a new house.

2). Whether, but not if, is used before infinitives.

They can't decide whether to get married now or wait.

3). Whether is generally preferred in a two - part question with or.

The Directors have not decided whether they will recommend a dividend or reinvest the profits.

4). Use Whether when only 2 choices exist
I am not sure whether I could go.

As per American Oxford dictionary:
Use if for a conditional idea, whether for an alternative or possibility.