When versus Whenever
Whenever in doubt, use when.
If that doesn't suffice as a grammar rule for you, keep reading.
Whenever should be used in conjunction with statements representing indefinite time, statements applying to more than one time, or statements needing a general adverb, exempli gratia:
"Whenever I go to the movies, I get extra butter on my popcorn."
In this case, whenever applies to all times I go to the movies.
"Come over to my house whenever you want."
Whenever, in this case, is not a specific time.
"I eat whenever I am hungry."
Because I am hungry at more than one time, I use whenever as a general adverb.
When should be used with phrases of definite time, exempli gratia:
"When I go to the movies, I will get extra butter on my popcorn."
"When I went to the movies, I got extra butter on my popcorn."
In the above sentences, when pertains to definite times of going to the movies.
"Come over my house when you need help."
When, in the above sentence, tells of the time during which "you need help."
This is a specified time, and therefore calls for the use of the word when.
"When I am hungry I will eat."
When, in this case, pertains to the time in which "I am hungry."
The use of the word will specifies time, and therefore when is used.
If that made no sense to you, then go with my first rule: Whenever in doubt, use when.
There is no basis for my rule, except I've heard whenever overused way too much lately. That's also the motivation behind this post. I find whenever annoying, now. Here are some commonly heard negative examples, which illustrate the wrong way to use whenever:
"Do you remember whenever I was in the car with you yesterday?"
The time is specified by the other words in the sentence.
"Whenever I was younger, I had a dog."
Granted, he or she may not remember when the dog was had,
but younger specifies enough to need when instead of whenever.
When when is wrongfully used in place of whenever I barely notice, whereas when whenever is used when the word should be when it sends a cacophonous ringing through my ears. So, just use when all the time, if you can't remember the rules.
Sorry for being anal-retentive,
P.S. I think grammar is one of my favorite topics for writing. There will probably be more grammar-snob posts to come.