and mass 
approximately 
times the mass of a proton. [P3.3, P8.1]
is: an elementary particle that is a constituent of every atom. [P3.3, P8.1]
has: charge and mass approximately times the mass of a proton. [P3.3, P8.1]
is liberated: from atoms when the atoms are ionized in a discharge tube, as deduced by its discoverer J.J. Thomson (1856-1940). [P8.1]
has: no known internal structure at the time of this writing. [P8.1]
Copyright 1997, The Open University