It's a common misconception that "whether" has to go with "or not." It's true that only whether CAN go with "or not" but whether doesn't HAVE to go with or not.

The easier way to understand the difference between "if" and "whether" is this:

If they both sound ok, use whether.

Really! It always works!

"I don't know if he's going to the beach today."
"I don't know whether he's going to the beach today."
They both sound ok, right? So "whether" is right.

Compare that to:
"If it's sunny, I'll go to the beach today."
"Whether it's sunny, I'll go to the beach today."

Whew! In that case, clearly "whether" makes no sense! So say "if."

If that rule doesn't work for you, here's a more "official" definition:

Use if only in conditional statements. Use whether the rest of the time.

Hope that helps,
Laura

Thanks Laura..for a great explanation!!

Happy Turkey day