Integers in the Wolfram Language are atomic expressions, while uses of the Map function are not atomic.
But if you didn't know this, how could you find out using only the Wolfram Language? The best I can do is something like:
In := AtomQ[Map] Out = True
But Wolfram isn't telling me that Map expressions are atomic. They aren't. It's Map itself, the symbol, which is atomic, and that's what Wolfram is talking about.
So how can I ask if a hypothetical expression with a particular head would be atomic. The answer should True for Integer, but false for Map.
Edit: It looks like the way I want to do things isn't possible within the language. I've written another question here that's more general, hopefully to elicit a way to do this I haven't imagined.