3.5 The mass of an atom is concentrated in its nucleus JJ proposed the plum- Thomson 's Model of the atom pudding model" for atoms Positive charge spread over the entire sphere Thomson proposed that the atoms might be made of thousands of tiny, negatively charged particles swarming within a cloud of positively charge, much like plums and raisins in an old fashioned christmas plum- pudding3.5 The mass of an atom is concentrated in its nucleus JJ proposed the “plum￾pudding model” for atoms. Thomson proposed that the atoms might be made of thousands of tiny ,negatively charged particles swarming within a cloud of positively charge, much like plums and raisins in an old￾fashioned christmas plum￾pudding