a charged particle in an accelerated motion produces em radiation.
in an atom the electrons have accelerated motion. does it means that all electrons in atoms produce em

Yes. all the accelerating charged electron particles produces the Electromagnetic wave.  

Explanation:

Magnetic fields are produced during the movement of the charged particle. the magnetic field produced, will exert some force in the moving charges. The electric field as well as the magnetic field travelling in the empty space with respect of speed of light are the electromagnetic wave. Moving electron will always produce the magnetic field and thus the electrons motion are constant,but when the acceleration starts the electromagnetic waves are being radiated.

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.