What is the smallest and largest wavelength in electromagnetic radiation?

Answer

The division of the electromagnetic spectrum itself into areas, ranging from gamma, over X-ray, UV, infrared, microwaves to radio, is actually man-made. For nature it is always about the same creatures: photons.
But this division is of course not done arbitrarily: although it has developed in part historically, it is certainly also partly linked to the physical processes that underlie the origin of certain types of radiation.
Man himself has also influenced this division. Why do we distinguish between UV and visual blue light, (or between infrared and visual red light) ? Because we can always see one and not the other. And because our atmosphere blocks UV light and infrared, and visual light does not. These two reasons are, of course, linked. But an alien civilization that could see infrared light would extend their “visual” range to a wavelength well above our line between visual and IR.
The wavelength of photons varies by a factor of 10²⁰, so it is very easy to understand that there are completely different reasons why a photon is a gamma photon, or a radio photon. The difference is a gamma wave and a radio wave is not in what they are, but in how they arise. Due to the enormous differences in energy, the techniques for observing them are also profoundly different.
Now to answer your own question:
We define all EM radiation with a frequency greater than a certain limit as
“gamma” radiation. So, no, there is no radiation that is more energetic than gamma radiation because we have defined gamma radiation as the most energetic. In the same way, radio radiation is the least energetic form of EM radiation. But again, these “large” wavelength ranges are still divided into smaller subregions.
I did some searching and found an interesting answer to a very similar question on a similar Nasa forum.

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970412e.html