There Are Electrons in Atoms! I t is important to give studellts t,he real and convincing proof that atoms contain electrons. The evidence provided by most e1ementar.v textbooks is the emission of electrons by met,& in vamnm discharge and in photoelectric and thermionic effects. Does the emia~ionof electrons by rather drastic conditions really prove the presence of electrons in atoms? Such an argument is like the conclusion that there is smoke in x gun before a shot because it is evolved from the barrel after the shot. Let us remember that o ferr decades ago it was assumed that the emission of elcctrans in radioactive decay proves the presencc of electrons in atomio nuclei. re now know that this assumption was wrong. Phenomena do exist which prove uarqnivorally that electrons are not onl?-emitted from atoms but really are contained in them. The Zeeman effect is an example of such direct evidence. I have found the following discltfifiion to be effective: First, I remind the students that electromagnetic wave8 (such ss those used in radio and television oommunicrttion) are generated by the displacement of ~lert,rical charges and that light waves are the same type of elretromagnetie vibrations differing only in frequency (or wave length). Then I remind then, that all elemenrary substances and compounds of a n element emit light of characteristic frequency or freqoeneief. This unique property for each kind of atom means that the same kind of displscement oi electrical rharge must take place. After that I describe the Zeeman effect and point out that a magnetic field changes the conditions of displacement of electrical charges. Then I show that, according to the laws of electrodynamics, the obswverl di~plaeemrntof the frequency and the magnitude of the magnetic field allow one to calculate the ratio of rharge to mass (e/n~)of t,he charged particle wit,hin the atom which is moving t o generate the light,. The fact that this ratio turns out t o be identical with that calculated for frec electrons by other methods is convincing proof that electrons are indeed nithin the stom. . ~ A T O LSEMENTSOV
LAFAYETTE COLLEGE ELSTON,PENNSYL~ANLI
22 / Journd of Chemical Educotion
