I checked your site but can’t find the information I need. How can I explain the correct usages of “if…not” and “unless”?

I’ll go to the game if it doesn’t rain.
I’ll go to the game unless it rains.
(both OK, right?)

I’d like her if she didn’t wear so much make up.
I’d like her unless she didn’t wear so much make up.
(the second sentence is wrong, right?)

What’s/what are the rules for using these?

I’ve been asked and I’d REALLY appreciate your help!!

Dear Mr. E:

The word “unless” is actually a negative. (“Lest” is the somewhat old-fashioned positive). The second sentence in your second set is really a double negative. Double negatives are considered ungrammatical and confusing. That last sentence is a bit confusing…