I understand that the electromagnetic spectrum is made up of different frequencies of light waves, but is this true in all cases such as with longer wave frequencies? "such as with microwaves". sometimes I get the impression that with microwave ovens for example use waves of electrons, so my question is, is there some kind of threshold where somewhere between infrared to microwaves does the frequency makes the conversion from light to electrons? (and if so, how?) or is it always light and has some other correlation such as light influencing the electrons thru the air?
All electromagnetic waves (long wave, radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays) are produced when electrons are accelerated (not necessarily transmitted).
Electrons themselves are not transmitted and thought of as electromagnetic waves in most of the spectrum except in the case of x-rays, or synchrotron radiation. In the case of x-rays, of course, the electrons themselves have been accelerated towards a target, as in an x-ray or an electron microscope (and this just happens to correspond to a particular energy on the electromagnetic spectrum that is between UV and gamma radiation).
UV and energies above are also known as ionizing radiation, because this area of the high EM spectrum is sufficiently energetic to strip valence electrons from atoms and thereby effect chemical (and not just thermal) changes.
This is actually a good (and a little tricky) question about the EM spectrum.