If vs Whether

What is the difference between “if” and “whether”? Many thanks for considering my request. Mirco

That’s a difficult question! Generally speaking, if it’s a simple phrase (or a conditional) you use “if”: “If you want to save money, you need to spend less,” “If you say that again, I will kill you” but when it’s proceeded by a verb like “to know”, then “whether” is better. For example, many people say, “I don’t know if you heard the news” but it’s grammatically correct to say, “I don’t know whether you heard the news.” In speech this error is almost acceptable but:
“If you wrote something like that on a job or university application, then it wouldn’t look very good!”
“I don’t know whether you wrote something like that on a job or university application, but I hope you didn’t!”