As the chemical properties of the elements were known to largely repeat themselves according to the periodic law, in 1919 the American chemist Irving Langmuir suggested that this could be explained if the electrons in an atom were connected or clustered in some manner.
Unha vez que xa se sabía que as propiedades químicas dos elementos se repetian de acordo coa lei periódica, en 1919 o químico norteamericano Irving Langmuir suxeriu que isto podía ser explicado se os electróns dun átomo estivesen dalgún xeito conectados.