When and whenever differ in meaning as well as use in sentences.
Difference in meaning
When usually tells that a situation happens once:
I bought the car when I received my first salary.
Whenever tells that a situation is repeated:
They come here whenever they feel like it.
Do your breathing exercises whenever possible.
Though less preferred, when too can represent a repeated situation:
They come here when they feel like it.
Do your breathing exercises when possible.
Though rarely, whenever can be used in place of when to add emphasis – and sometimes surprise as well. Examples:
When do you come up with such creative ideas?
Whenever do you come up with such creative ideas? [Whenever lends emphasis.]
Difference in use in sentences
They’re used differently in sentences, while retaining their meaning we just saw.
In independent clauses
When is used as an interrogative adverb in independent clauses. Whenever though is rarely used in such way. Examples:
When did you first notice the problem? [As interrogative adverb]
In dependent clauses
When can introduce noun, relative, and adverb clause, functioning as interrogative adverb, relative adverb, and subordinating conjunction, respectively. Whenever can introduce adverb clause, functioning as subordinating conjunction. Examples:
When the meeting will start is still uncertain. [As interrogative adverb in noun clause]
The moment when they announced the winner was thrilling. [As relative adverb in relative clause]
When the sun sets, the sky turns a beautiful shade of orange. [As subordinating conjunction in adverb clause]
Whenever they host a party, the neighbors come over. [As subordinating conjunction in adverb clause]
As subordinating conjunction, only when can be pre-modified by focusing adverbs such as just, right, only, exactly, precisely, simply, specifically, and strictly. Examples:
Exactly when the sun sets, the sky turns a beautiful shade of orange.
Exactly whenever they host a party, the neighbors come over. [Incorrect]
