What follows is a brief list of benchmarks and discoveries that shaped our ideas on atoms and nuclei. ... Discovery of electrons . ... Comparing this to Faraday's results, one could get " Avogadro's number ", the number of (say) hydrogen atoms in one gram of hydrogen--an enormously large number. ... Similarly, energized atoms are only allowed to exist in one of a number of energy levels. ... By the way, Avogadro's number is 602,000,000,000,000,000,000,000 (6.02 10 23 ) molecules in 1 gr hydrogen. ...